chore(package): update dart-sass to version 1.13.2

Author: greenkeeper[bot]

package.json

@@ -12,7 +12,7 @@
   "devDependencies": {
     "autoprefixer": "9.1.5",
     "cssnano": "4.1.0",
-    "dart-sass": "1.13.1",
+    "dart-sass": "1.13.2",
     "fibers": "3.0.0",
     "grunt": "~1",
     "grunt-cli": "~1",