Add -loader suffix in webpack, closes #2410

[QWp6t]

Bundled builds were not being built correctly..

Example: https://github.com/yarnpkg/yarn/releases/download/v0.19.0/yarn-0.19.0.js
Issue: #2410

tl;dr

Just add -loader suffix to loaders in to scripts/build-webpack.js. ezpz

Details

Previously, packages named with -loader suffix could be specified as loaders within Webpack without requiring the suffix to be named explicitly. Webpack 2.1.0-beta.26 no longer looks for -loader suffix automatically, and packages have to therefore be named explicitly or -loader can be added to resolveLoader.moduleExtensions.

See: https://github.com/webpack/webpack/releases/tag/v2.1.0-beta.26

This PR explicitly adds -loader suffix, and now bundles are correctly built.

Before

~/yarn-0.19.0  (yarn@0.19.0)
λ node scripts/build-webpack.js
[]

~/yarn-0.19.0  (yarn@0.19.0)
λ

After

~/yarn-0.19.0  (yarn@0.19.0)
λ node scripts/build-webpack.js
[ 'node_modules/ansi-escapes/index.js',
  'node_modules/ansi-regex/index.js',
  'node_modules/ansi-styles/index.js',
  'node_modules/array-find-index/index.js',
  'node_modules/asn1/lib/ber/errors.js',
  # ... etc ...
  'src/util/promise.js',
  'src/util/request-manager.js',
  'src/util/stream.js',
  'src/util/version.js' ]

~/yarn-0.19.0  (yarn@0.19.0)
λ

[bestander]

Thanks, cherry-picking to 0.19.
0.19.1 will be released next week