Update file-loader to the latest version 🚀 (#1193)

## The devDependency [file-loader](https://github.com/webpack-contrib/file-loader) was updated from `2.0.0` to `3.0.0`.
This version is **not covered** by your **current version range**.

If you don’t accept this pull request, your project will work just like it did before. However, you might be missing out on a bunch of new features, fixes and/or performance improvements from the dependency update.

---

<details>
<summary>Release Notes for v3.0.0</summary>

<p><a name="user-content-3.0.0"></a></p>
<h1><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/compare/v2.0.0...v3.0.0">3.0.0</a> (2018-12-20)</h1>
<h3>Code Refactoring</h3>
<ul>
<li>drop support for webpack &lt; 4 (<a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/issues/303" data-hovercard-type="pull_request" data-hovercard-url="/webpack-contrib/file-loader/pull/303/hovercard">#303</a>) (<a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/203a4ee">203a4ee</a>)</li>
<li>more validations in <code>options</code> schema</li>
</ul>
<h3>Features</h3>
<ul>
<li><code>resourcePath</code> is now available in <code>outputPath</code> and <code>publicPath</code> (<a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/issues/304" data-hovercard-type="pull_request" data-hovercard-url="/webpack-contrib/file-loader/pull/304/hovercard">#304</a>) (<a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/0d66e64">0d66e64</a>)</li>
<li><code>context</code> is now available in <code>outputPath</code> and <code>publicPath</code> (<a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/issues/305" data-hovercard-type="pull_request" data-hovercard-url="/webpack-contrib/file-loader/pull/305/hovercard">#305</a>) (<a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/d5eb823">d5eb823</a>)</li>
</ul>
<h3>BREAKING CHANGES</h3>
<ul>
<li>removed the <code>useRelativePath</code> option. It is dangerously and break url when you use multiple entry points.</li>
<li>drop support for webpack &lt; 4</li>
</ul>
</details>

<details>
<summary>Commits</summary>
<p>The new version differs by 10 commits.</p>
<ul>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/40a206e71c83eed2bf4f06a887a2f7e60ad374dc"><code>40a206e</code></a> <code>chore(release): 3.0.0</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/269d3fb92cba30d5e141fb62c6b1274524c4fb69"><code>269d3fb</code></a> <code>docs: improve README (#307)</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/9853db124d3e41e37a46725660c7fdacd896d091"><code>9853db1</code></a> <code>refactor: loader</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/d5eb8234c0304f6cd75c8176bfad9532358427e9"><code>d5eb823</code></a> <code>feat: <code>context</code> is now available in <code>outputPath</code> and <code>publicPath</code> (#305)</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/0d66e64f0c3d825662f0ab7a00c859b84f873302"><code>0d66e64</code></a> <code>feat: <code>resourcePath</code> is now available in <code>outputPath</code> and <code>publicPath</code> (#304)</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/203a4ee55aa7ff99588ff86fbf5cdb9e4cafadf1"><code>203a4ee</code></a> <code>refactor: drop support for webpack &lt; 4 (#303)</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/e5fe4e8048aa91b3f95af11841c609169c926e52"><code>e5fe4e8</code></a> <code>refactor: tests (#302)</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/3981acc6eae9287314c9f14de16817ef0de1d69d"><code>3981acc</code></a> <code>refactor: update <code>defaults</code> (#301)</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/85230c9a34ea78a7c55265577417f2303b4d01a0"><code>85230c9</code></a> <code>FIx formatting for "Contributing" and "MIT" (#298)</code></li>
<li><a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/commit/6631d3991d7031bd9ef52fa774e76f7da73343e4"><code>6631d39</code></a> <code>docs(changelog): fix typo</code></li>
</ul>
<p>See the <a href="https://urls.greenkeeper.io/webpack-contrib/file-loader/compare/8d43c38bd023719e3c270d431131d45ceafa2929...40a206e71c83eed2bf4f06a887a2f7e60ad374dc">full diff</a></p>
</details>

<details>
  <summary>FAQ and help</summary>

  There is a collection of [frequently asked questions](https://greenkeeper.io/faq.html). If those don’t help, you can always [ask the humans behind Greenkeeper](https://github.com/greenkeeperio/greenkeeper/issues/new).
</details>

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package.json

@@ -126,7 +126,7 @@
     "extract-loader": "^3.0.0",
     "fancy-log": "^1.3.2",
     "fetch-mock": "^7.2.5",
-    "file-loader": "^2.0.0",
+    "file-loader": "^3.0.0",
     "gulp": "^4.0.0",
     "gulp-babel": "8.0.0",
     "gulp-newer": "^1.4.0",