chore(package): update prettier to version 2.0.4

Closes #26

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
     "eslint-plugin-standard": "^4.0.0",
     "jest": "^24.8.0",
     "jsinspect": "^0.12.7",
-    "prettier": "^1.17.1"
+    "prettier": "^2.0.4"
   },
   "keywords": [
     "validation"