.gitconfig: Make sure go never overrides branches

Closes #357. Thanks to @yukideluxe!

.gitconfig

@@ -14,7 +14,7 @@
 	# Commit all changes
 	ca = !git add -A && git commit -av
 	# Switch to a branch, creating it if necessary
-	go = checkout -B
+	go = "!f() { git checkout -b \"$1\" 2> /dev/null || git checkout \"$1\"; }; f"
 	# Show verbose output about tags, branches or remotes
 	tags = tag -l
 	branches = branch -a