Update dependency postcss-loader to v7.1.0

Author: renovate[bot]

package-lock.json

@@ -45,7 +45,7 @@
     "less": "4.1.3",
     "less-loader": "11.1.0",
     "node-sass": "8.0.0",
-    "postcss-loader": "7.0.2",
+    "postcss-loader": "7.1.0",
     "rimraf": "4.4.0",
     "sass-loader": "13.2.0",
     "style-loader": "3.3.2",