chore(package): update sass-loader to version 7.3.1

Closes #67

Author: greenkeeper[bot]

Diff for: package.json

@@ -34,7 +34,7 @@
     "node-sass": "^4.12.0",
     "resolve-url-loader": "3.1.0",
     "rimraf": "2.6.3",
-    "sass-loader": "7.1.0",
+    "sass-loader": "7.3.1",
     "style-loader": "0.23.1",
     "ts-loader": "^6.0.1",
     "tslib": "1.9.3",