fix(git-bulk): bad test operator

With the Bash' regexp matching operator `=~`, we need to use the Bash
conditional expression evaluation command `[[ ]]`.

Author: Pierre Ayoub

bin/git-bulk

@@ -174,7 +174,7 @@ function executBulkOp () {
       local curdir=$PWD
       local leadingpath=${curdir#"${actual}"}
       # do not execute if we do not want to consider a ".git" directory under a hidden directory
-      if [ $no_follow_hidden = false ] || ! [ "$leadingpath" =~ "/." ]; then
+      if [ $no_follow_hidden = false ] || ! [[ "$leadingpath" =~ "/." ]]; then
         guardedExecution "$@"
       fi
       cd "$rwsdir" || exit 1 # back to origin location of last find command