Properly retrieve and parse the app name from git remote

contrib/dokku_client.sh

@@ -3,8 +3,17 @@ set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
 
 if [[ ! -z $DOKKU_HOST ]]; then
 	function dokku {
-		appname=$(git remote -v 2>/dev/null | grep dokku | head -n 1 | cut -f1 -d' ' | cut -f2 -d':' 2>/dev/null)
-		if [[ "$?" != "0" ]]; then
+		appname=""
+		if [ -d .git ] || git rev-parse --git-dir > /dev/null 2>&1; then
+			set +e
+			appname=$(git remote -v 2>/dev/null | grep -Ei "^dokku" | head -n 1 | cut -f1 -d' ' | cut -f2 -d':' 2>/dev/null)
+			set -e
+		else
+			echo "This is not a git repository"
+			exit 1
+		fi
+
+		if [[ "$appname" != "" ]]; then
 			donotshift="YES"
 		fi