chore(package): update prettier to version 2.0.4

Closes #36

Author: greenkeeper[bot]

package.json

@@ -82,7 +82,7 @@
         "karma-webpack": "^3.0.5",
         "mocha": "^5.2.0",
         "phaser": "^3.16.2",
-        "prettier": "^1.16.4",
+        "prettier": "^2.0.4",
         "publish-please": "^5.4.3",
         "remap-istanbul": "^0.13.0",
         "rimraf": "^2.6.3",