Update correct test command in contributing docs (#1377)

Co-authored-by: Taranjeet <Taranjeet Singh>
Co-authored-by: Anton Pirker <anton.pirker@sentry.io>

Author: targhs

CONTRIBUTING.md

@@ -74,7 +74,7 @@ So the simplest way to run tests is:
 ```bash
 cd sentry-python
 
-make tests
+make test
 ```
 
 This will use [Tox](https://tox.wiki/en/latest/) to run our whole test suite