chore(package): update dart-sass to version 1.15.2

Author: greenkeeper[bot]

package.json

@@ -21,7 +21,7 @@
     "clean-webpack-plugin": "1.0.0",
     "cross-env": "5.2.0",
     "css-loader": "1.0.1",
-    "dart-sass": "1.15.1",
+    "dart-sass": "1.15.2",
     "fibers": "3.1.1",
     "mini-css-extract-plugin": "0.4.5",
     "postcss-loader": "3.0.0",