docs: tutorials: rolling alice: coach alice: our open source guide: Support earlier versions of git by getting branch name without --show-current

Author: pdxjohnny

docs/tutorials/rolling_alice/0001_coach_alice/0002_our_open_source_guide.md

@@ -47,7 +47,7 @@ $ cd my-new-python-project
 $ echo 'print("Hello World")' > test.py
 $ git add test.py
 $ git commit -sam 'Initial Commit'
-$ git push --set-upstream origin $(git branch --show-current)
+$ git push --set-upstream origin $(git branch -r | sed -e 's/.*\///')
 $ cd ..
 $ rm -rf my-new-python-project
 ```