Update yarn next script with --enable-source-maps

[styfle]

This will allow for easier development. For example, when running yarn next dev examples/basic-css and an internal is error is thrown, you'll see the TS source file in the stack trace instead of the JS dist file.

[ijjk]

Stats from current PR

Default Server Mode (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
buildDuration	15.1s	15s	-71ms
buildDurationCached	4.2s	4.1s	-91ms
nodeModulesSize	46.6 MB	46.7 MB	⚠️ +89.7 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.756	2.773	⚠️ +0.02
/ avg req/sec	907.17	901.7	⚠️ -5.47
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.607	1.567	-0.04
/error-in-render avg req/sec	1555.42	1595.69	+40.27

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
framework-HASH.js gzip	39.3 kB	39.3 kB	✓
main-HASH.js gzip	19.4 kB	19.4 kB	✓
webpack-HASH.js gzip	994 B	994 B	✓
Overall change	59.7 kB	59.7 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
_app-HASH.js gzip	1.02 kB	1.02 kB	✓
_error-HASH.js gzip	3.06 kB	3.06 kB	✓
amp-HASH.js gzip	526 B	526 B	✓
css-HASH.js gzip	334 B	334 B	✓
hooks-HASH.js gzip	890 B	890 B	✓
index-HASH.js gzip	262 B	262 B	✓
link-HASH.js gzip	1.65 kB	1.65 kB	✓
routerDirect..HASH.js gzip	331 B	331 B	✓
withRouter-HASH.js gzip	329 B	329 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	8.54 kB	8.54 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
_buildManifest.js gzip	390 B	390 B	✓
Overall change	390 B	390 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
index.html gzip	560 B	560 B	✓
link.html gzip	568 B	568 B	✓
withRouter.html gzip	556 B	556 B	✓
Overall change	1.68 kB	1.68 kB	✓

---

Serverless Mode

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
buildDuration	17.7s	17.7s	-49ms
buildDurationCached	5.2s	5.1s	-38ms
nodeModulesSize	46.6 MB	46.7 MB	⚠️ +89.7 kB

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
framework-HASH.js gzip	39.3 kB	39.3 kB	✓
main-HASH.js gzip	19.4 kB	19.4 kB	✓
webpack-HASH.js gzip	994 B	994 B	✓
Overall change	59.7 kB	59.7 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
_app-HASH.js gzip	1.02 kB	1.02 kB	✓
_error-HASH.js gzip	3.06 kB	3.06 kB	✓
amp-HASH.js gzip	526 B	526 B	✓
css-HASH.js gzip	334 B	334 B	✓
hooks-HASH.js gzip	890 B	890 B	✓
index-HASH.js gzip	262 B	262 B	✓
link-HASH.js gzip	1.65 kB	1.65 kB	✓
routerDirect..HASH.js gzip	331 B	331 B	✓
withRouter-HASH.js gzip	329 B	329 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	8.54 kB	8.54 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
_buildManifest.js gzip	390 B	390 B	✓
Overall change	390 B	390 B	✓

Serverless bundles Overall increase ⚠️

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
_error.js	16.9 kB	16.9 kB	✓
404.html	2.42 kB	2.42 kB	✓
500.html	2.41 kB	2.41 kB	✓
amp.amp.html	10.8 kB	10.8 kB	✓
amp.html	1.61 kB	1.61 kB	✓
css.html	1.79 kB	1.79 kB	✓
hooks.html	1.67 kB	1.67 kB	✓
index.js	17.2 kB	17.2 kB	✓
link.js	17.4 kB	17.4 kB	✓
routerDirect.js	17.4 kB	17.4 kB	✓
withRouter.js	17.4 kB	17.4 kB	⚠️ +2 B
Overall change	107 kB	107 kB	⚠️ +2 B

---

Webpack 4 Mode

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
buildDuration	13.6s	13.8s	⚠️ +131ms
buildDurationCached	5.7s	5.6s	-152ms
nodeModulesSize	46.6 MB	46.7 MB	⚠️ +89.7 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.797	2.849	⚠️ +0.05
/ avg req/sec	893.95	877.48	⚠️ -16.47
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.666	1.647	-0.02
/error-in-render avg req/sec	1500.84	1517.95	+17.11

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
677f882d2ed8..HASH.js gzip	13.3 kB	13.3 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-HASH.js gzip	7.25 kB	7.25 kB	✓
webpack-HASH.js gzip	751 B	751 B	✓
Overall change	60.3 kB	60.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
polyfills-HASH.js gzip	31.3 kB	31.3 kB	✓
Overall change	31.3 kB	31.3 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
_app-HASH.js gzip	1.28 kB	1.28 kB	✓
_error-HASH.js gzip	3.74 kB	3.74 kB	✓
amp-HASH.js gzip	536 B	536 B	✓
css-HASH.js gzip	339 B	339 B	✓
hooks-HASH.js gzip	887 B	887 B	✓
index-HASH.js gzip	227 B	227 B	✓
link-HASH.js gzip	1.64 kB	1.64 kB	✓
routerDirect..HASH.js gzip	303 B	303 B	✓
withRouter-HASH.js gzip	302 B	302 B	✓
e025d2764813..52f.css gzip	125 B	125 B	✓
Overall change	9.38 kB	9.38 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
_buildManifest.js gzip	420 B	420 B	✓
Overall change	420 B	420 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js styfle/enable-source-maps	Change
index.html gzip	613 B	613 B	✓
link.html gzip	620 B	620 B	✓
withRouter.html gzip	606 B	606 B	✓
Overall change	1.84 kB	1.84 kB	✓

Commit: dee205e