Update prettier to version 1.18.0 (#281)

Author: greenkeeper[bot]

package.json

@@ -38,7 +38,7 @@
     "eslint-config-problems": "2.0.0",
     "nyc": "^14.0.0",
     "postcss-import": "^12.0.0",
-    "prettier": "~1.17.0",
+    "prettier": "~1.18.0",
     "sugarss": "^2.0.0",
     "uuid": "^3.0.1"
   },