postcss-modules-scope incompatible with PostCSS v5.x

Simple fix for webpack-contrib#691

Author: mikeumus

package.json

@@ -20,7 +20,7 @@
     "loader-utils": "^1.0.2",
     "lodash.camelcase": "^4.3.0",
     "object-assign": "^4.1.1",
-    "postcss": "^5.0.6",
+    "postcss": "^6.0.23",
     "postcss-modules-extract-imports": "^1.2.0",
     "postcss-modules-local-by-default": "^1.2.0",
     "postcss-modules-scope": "^1.1.0",