chore(package): update mocha to version 6.1.3

Closes #21

Author: greenkeeper[bot]

package.json

@@ -85,7 +85,7 @@
         "karma-sourcemap-loader": "^0.3.7",
         "karma-sourcemap-writer": "^0.1.2",
         "karma-webpack": "^3.0.5",
-        "mocha": "^5.2.0",
+        "mocha": "^6.1.3",
         "phaser": "^3.16.2",
         "prettier": "^1.16.4",
         "publish-please": "^5.4.3",