Fix contributor generation command

CONTRIBUTING.rst

@@ -760,7 +760,7 @@ To make a new 3.4 release::
     # - update the date
     # - look for typos
     # - add list of contributors via `python3 scripts/get-contributions-stats.py $NEXT_RELEASE`
-    git log $PREVIOUS_RELEASE.. --format="%aN" --reverse | sort | uniq -u # Get all commit authors since last release
+    git log $PREVIOUS_RELEASE.. --format="%aN" --reverse | sort | uniq  # Get all commit authors since last release
     nano CHANGELOG
 
     # Set the `__version__` variable to $NEXT_RELEASE