chore(package): update mocha to version 4.0.0 (babel#524)

Author: greenkeeper[bot]

package.json

@@ -45,7 +45,7 @@
     "espree": "^3.4.0",
     "husky": "^0.14.0",
     "lint-staged": "^4.0.0",
-    "mocha": "^3.0.0",
+    "mocha": "^4.0.0",
     "prettier": "^1.4.4"
   },
   "lint-staged": {