bug #406 Fix the mini-css-extract-plugin 0.4.3 issue and increase min. allowed Webpack version (Lyrkan)

This PR was merged into the master branch.

Discussion
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Fix the mini-css-extract-plugin 0.4.3 issue and increase min. allowed Webpack version

This PR fixes both of the issues detected in #403:

- Set the maximum allowed version for `mini-css-extract-plugin` to 0.4.2 (since 0.4.3 doesn't work with the current version of the webpack-manifest-plugin, see #404). This is a temporary solution, once it's fixed (either in mini-css-extract-plugin or in weback-manifest-plugin) we'll have to change it again.

- Set the minimum allowed version for `webpack` to 4.20.0. The previous one (4.0.0) seemed to break `mini-css-extract-plugin` (see https://travis-ci.org/Lyrkan/webpack-encore/jobs/439810002).

Commits
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04f42af Temporary fix for the mini-css-extract-plugin 0.4.3 issue

Author: weaverryan

package.json

@@ -38,15 +38,15 @@
     "fs-extra": "^2.0.0",
     "loader-utils": "^1.1.0",
     "lodash": ">=3.5 <5",
-    "mini-css-extract-plugin": "^0.4.0",
+    "mini-css-extract-plugin": ">=0.4.0 <0.4.3",
     "pkg-up": "^1.0.0",
     "pretty-error": "^2.1.1",
     "resolve-url-loader": "^2.3.0",
     "semver": "^5.5.0",
     "style-loader": "^0.21.0",
     "tmp": "^0.0.33",
     "uglifyjs-webpack-plugin": "^1.2.5",
-    "webpack": "^4.0.0",
+    "webpack": "^4.20.0",
     "webpack-chunk-hash": "^0.6.0",
     "webpack-cli": "^3.0.0",
     "webpack-dev-server": "^3.1.4",