chore(package): update mocha to version 6.2.1

Closes #46

package.json

@@ -43,7 +43,7 @@
     "devDependencies": {
         "coveralls": "~3.0.3",
         "istanbul": "~0.4.5",
-        "mocha": "~6.1.4",
+        "mocha": "~6.2.1",
         "mocha-lcov-reporter": "~1.3.0",
         "request": "~2.88.0"
     }