chore(package): update postcss-loader to version 2.1.3

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "file-loader": "1.1.11",
     "node-sass": "4.8.3",
     "on-build-webpack": "0.1.0",
-    "postcss-loader": "2.1.2",
+    "postcss-loader": "2.1.3",
     "sass-loader": "6.0.7",
     "style-loader": "0.20.3",
     "stylelint": "9.1.3",