Fix typo in CONTRIBUTING.md (#108)

We just `cd`'ed into `python`, thus we should remove it from the path.

Co-authored-by: Stephen Xie <stephen29xie@gmail.com>

Author: MiWeiss

CONTRIBUTING.md

@@ -27,7 +27,7 @@ There are some nuances to building the Voyager python code.  Please read on for
 For basic building, you should be able to simply run the following commands:
 ```shell
 cd python
-pip install -r python/dev-requirements.txt
+pip install -r dev-requirements.txt
 pip install .
 ```