adding a git commit --amend --no-edit alias

I sometimes want this, but not often enough that I can think of a good
alias name for it, especially one that doesn't conflict with `cia`.

I was considering `cane` (for Commit Amend No Edit), but for now I'm
going with `atc`, (for Add To Commit).

git/gitconfig.symlink

@@ -8,6 +8,7 @@
 	ci = commit
 	cia = !git add --all && git commit --all
 	cie = commit --allow-empty
+	atc = commit --amend --no-edit
 	co = checkout
 	staged = diff --cached
 	pending = diff --cached