Update DEVELOPMENT.md (tensorflow#1431)

Change the "help wanted" tag to "stat:contributions welcome"

Author: dsmilkov

DEVELOPMENT.md

@@ -57,5 +57,4 @@ To install it locally, run `yarn add ./tensorflow-tf-core-VERSION.tgz`.
 
 > On Windows, use bash (available through git) to use the scripts above.
 
-Looking to contribute, and don't know where to start? Check out our "help wanted"
-[issues](https://github.com/tensorflow/tfjs/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22).
+Looking to contribute, and don't know where to start? Check out our "stat:contributions welcome" [issues](https://github.com/tensorflow/tfjs/labels/stat%3Acontributions%20welcome).