Merge branch 're/completion-fix-test-equality'

Fix long-standing shell syntax error in the completion script.

* re/completion-fix-test-equality:
  completion: fix incorrect bash/zsh string equality check

contrib/completion/git-completion.bash

@@ -515,7 +515,7 @@ __gitcomp_file ()
 # argument, and using the options specified in the second argument.
 __git_ls_files_helper ()
 {
-	if [ "$2" == "--committable" ]; then
+	if [ "$2" = "--committable" ]; then
 		__git -C "$1" -c core.quotePath=false diff-index \
 			--name-only --relative HEAD -- "${3//\\/\\\\}*"
 	else