chore(package): update prettier to version 1.9.0

Author: greenkeeper[bot]

package.json

@@ -35,7 +35,7 @@
     "eslint-config-prettier": "^2.3.0",
     "eslint-plugin-prettier": "^2.3.0",
     "nyc": "^11.1.0",
-    "prettier": "~1.8.2",
+    "prettier": "~1.9.0",
     "rimraf": "^2.6.1",
     "semantic-release": "^10.0.0",
     "sinon": "^4.0.2",