Update prettier to version 1.9.0 (#322)

Author: greenkeeper[bot]

package.json

@@ -31,7 +31,7 @@
     "eslint-plugin-prettier": "^2.2.0",
     "npmpub": "^3.0.1",
     "postcss-scss": "^1.0.0",
-    "prettier": "1.8.2",
+    "prettier": "1.9.0",
     "sugarss": "^1.0.0"
   },
   "scripts": {