chore(package): update prettier to version 1.9.0

Author: greenkeeper[bot]

package.json

@@ -40,7 +40,7 @@
     "nock": "^9.1.0",
     "nyc": "^11.2.1",
     "p-retry": "^1.0.0",
-    "prettier": "~1.8.2",
+    "prettier": "~1.9.0",
     "semantic-release": "^10.0.0",
     "sinon": "^4.1.2",
     "tempy": "^0.2.1",