chore(package): update prettier to version 2.0.4

Closes #31

Author: greenkeeper[bot]

package.json

@@ -59,7 +59,7 @@
     "eslint-plugin-prettier": "3.1.0",
     "nodemon": "1.19.1",
     "nyc": "14.1.1",
-    "prettier": "1.18.2",
+    "prettier": "2.0.4",
     "sinon": "7.4.1",
     "source-map-support": "0.5.13",
     "tap-xunit": "2.4.1",