The problem is that when sublimetext2 is started, it doesn’t block and immediately returns. Git then thinks that you’re done editing the file and performs the rebase. That’s why you see the
Successfully rebased and updated refs/heads/staging
message, before you even edited the file. Use the subl command instead, which is designed for such use. The github help tells you do configure it with
git config --global core.editor "subl -n -w"