chore: move @types/express to dependencies

[martinemmert]

We currently use this package within a package that is consumed by our applications through a shared runtime package (fig 1). Therefore our applications are not fond of express or next and don't include any types.

During the build process, Typescript will throw an error (fig 2) saying it can't find the types of express and advises us to install them.

// fig 1
// simplified dependency tree w/o node_modules/ directory
app-one
 └── next-runtime
  └── our-i18n-lib/
   └── next-i18next

app-two
 └── next-runtime
  └── our-i18n-lib/
   └── next-i18next

// fig 2
../../../node_modules/next-i18next/types.d.ts:11:25 - error TS7016: Could not find a declaration file for module 'express'. '/.../app-one/node_modules/express/index.js' implicitly has an 'any' type.
  Try `npm install @types/express` if it exists or add a new declaration (.d.ts) file containing `declare module 'express';`

11 import { Request } from 'express'
                           ~~~~~~~~~

After digging into this issue, we concluded that @types/express should be a regular dependency instead of a dev dependency.

The following two discussions do explain the reasons behind that:

• Consider moving @types packages from devDependencies to dependencies apollographql/apollo-client#713
• Why --save instead of --save-dev? microsoft/types-publisher#81

I published a fork of this package with @types/express as regular dependencies for testing purposes here: https://www.npmjs.com/package/next-i18next_express-types

[adrai]

is this still a problem with 5.0.0-beta.2 ? The express dependency should be gone with v5 🤷‍♂️

[isaachinman]

@adrai Yep, that's correct. We don't have a clear picture of when v5 will land in prod, though.