Update dependency css-loader to v7

Author: renovate[bot]

package.json

@@ -34,7 +34,7 @@
     "babel-preset-env": "1.7.0",
     "babel-preset-stage-3": "6.24.1",
     "cross-env": "5.2.0",
-    "css-loader": "0.28.11",
+    "css-loader": "7.1.2",
     "file-loader": "1.1.11",
     "html-webpack-plugin": "3.2.0",
     "vue-loader": "13.7.2",