chore(package): update node-sass to version 4.13.0

Closes #113

Author: greenkeeper[bot]

package.json

@@ -22,7 +22,7 @@
     "grunt-sass": "3.0.2",
     "grunt-sass-lint": "0.2.4",
     "load-grunt-tasks": "~5.0.0",
-    "node-sass": "4.10.0",
+    "node-sass": "4.13.0",
     "sass-lint": "1.13.1"
   },
   "dependencies": {