The last step before making our repo public is to delete all the API secrete keys from the file and from the git history.

git rm backend/config/environments.js

git add .
git commit

git filter-branch --force --index-filter 'git rm --cached --ignore-unmatch backend/config/environments.js' --prune-empty --tag-name-filter cat -- --all

git push origin master --force

Now, you have removed the old file and all the history associated with it. Now add the new file, and commit as regular.