chore(package): update mocha to version 6.1.4

Closes #91

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
   "devDependencies": {
     "js-yaml": "^3.7.0",
     "longjohn": "^0.2.12",
-    "mocha": "^4.0.0",
+    "mocha": "^6.1.4",
     "xml2js": "^0.4.16",
     "yeoman-assert": "^3.0.0",
     "yeoman-test": "^1.6.0"