chore(package): update mocha to version 6.0.0 (#32)

package.json

@@ -28,6 +28,6 @@
     "concat-stream": "~2.0.0",
     "derequire": "~2.0.3",
     "istanbul": "~0.4.5",
-    "mocha": "~5.2.0"
+    "mocha": "~6.0.0"
   }
 }