chore(package): update mocha to version 6.0.0

Author: greenkeeper[bot]

package.json

@@ -24,7 +24,7 @@
   },
   "homepage": "https://github.com/Gerhut/create-function#readme",
   "devDependencies": {
-    "mocha": "^5.0.0",
+    "mocha": "^6.0.0",
     "nyc": "^13.2.0",
     "should": "^13.0.1",
     "standard": "^12.0.0"