Prompt user only once for their commit message.

By using no-edit, git merge will automatically accept the message called
with it and no longer call $EDITOR.

I also shellescaped hotfix instead of using quotes. I feel that calling
this function results in the code being more explicit, because the coder
will easily recognize that the string is being shellescaped (rather than
relying on their knowledge of the effect of double quotes in bash).