chore(package): update yarn to version 0.19.1

https://greenkeeper.io/

package.json

@@ -146,7 +146,7 @@
     "tslint": "4.3.0",
     "tuling123-client": "0.0.1",
     "typescript": "2.1.5",
-    "yarn": "0.18.1"
+    "yarn": "0.19.1"
   },
   "files_comment__whitelist_npm_publish": "http://stackoverflow.com/a/8617868/1123955",
   "files": [