Update the style guide link

CONTRIBUTING.md

@@ -2,4 +2,4 @@
 
 We follow the [IPython Contributing Guide](https://github.com/ipython/ipython/blob/master/CONTRIBUTING.md).
 
-All source code is written in [TypeScript](http://www.typescriptlang.org/Handbook). See the [Style Guide](https://github.com/phosphorjs/phosphor/wiki/Style-Guide).
+All source code is written in [TypeScript](http://www.typescriptlang.org/Handbook). See the [Style Guide](https://github.com/jupyter/jupyterlab/wiki/TypeScript-Style-Guide).