fix(package): update style-loader to version 0.21.0

Author: greenkeeper[bot]

package.json

@@ -72,7 +72,7 @@
     "rollbar": "^2.3.2",
     "sass-loader": "^6.0.6",
     "sendmail": "^1.2.0",
-    "style-loader": "^0.20.0",
+    "style-loader": "^0.21.0",
     "url-loader": "^1.0.0",
     "webpack": "^4.0.0",
     "webpack-bundle-analyzer": "^2.9.2",