chore(package): update sass-loader to version 8.0.0

Closes #160

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
     "extract-loader": "2.0.1",
     "file-loader": "4.0.0",
     "node-sass": "4.9.4",
-    "sass-loader": "7.3.0",
+    "sass-loader": "8.0.0",
     "webpack": "4.35.2",
     "webpack-cli": "3.3.7",
     "webpack-dev-server": "3.3.1"