chore(package): update mocha to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -89,7 +89,7 @@
     "karma-sourcemap-loader": "^0.3.7",
     "karma-sourcemap-writer": "^0.1.2",
     "karma-webpack": "^2.0.4",
-    "mocha": "^3.5.3",
+    "mocha": "^4.0.0",
     "nyc": "^11.2.1",
     "prettier": "^1.7.0",
     "publish-please": "^2.3.1",