chore(package): update mocha to version 6.2.0 (#560)

Closes #489

package.json

@@ -82,7 +82,7 @@
     "karma-mocha-reporter": "^2.0.4",
     "karma-webpack": "^4.0.0",
     "karma-xml2js-preprocessor": "^0.0.3",
-    "mocha": "^5.2.0",
+    "mocha": "^6.2.0",
     "npm-run-all": "^4.1.2",
     "pre-commit": "^1.2.2",
     "ts-loader": "^4.1.0",