chore(package): update mocha to version 6.2.0

Closes #32

Author: greenkeeper[bot]

Diff for: package.json

@@ -33,7 +33,7 @@
     "coveralls": "^3.0.0",
     "eslint": "^5.0.0",
     "istanbul": "^0.4.4",
-    "mocha": "^5.0.0",
+    "mocha": "^6.2.0",
     "mocha-lcov-reporter": "^1.2.0",
     "recursive-readdir-sync": "^1.0.6",
     "webpack": "^4.0.0",