git_auto_update: Improved comparism with GPG fingerprint

Configured grep to compare againg fixed strings, not regexp

roles/git_auto_update/templates/update.sh

@@ -20,7 +20,7 @@ fi
 
 git fetch --tags > /dev/null;
 TAG=$(git tag --list | grep "^$PREFIX" | sort -r | head -n 1);
-if [ -z "$GPG_FINGERPRINT" ] || (git verify-tag --raw "$TAG" 2>&1 | grep " VALIDSIG $GPG_FINGERPRINT ") > /dev/null; then
+if [ -z "$GPG_FINGERPRINT" ] || (git verify-tag --raw "$TAG" 2>&1 | grep --fixed-strings " VALIDSIG $GPG_FINGERPRINT ") > /dev/null; then
   git reset --hard;
   git checkout -q "$TAG";
   chown -R "$DEST_USER:$DEST_GROUP" .;