chore: fix build badge missing link

Author: FUSAKLA

README.md

@@ -1,6 +1,6 @@
 # Prometheus Gitlab Notifier
 
-![CircleCI](https://img.shields.io/circleci/build/github/FUSAKLA/prometheus-gitlab-notifier)
+[![CircleCI](https://img.shields.io/circleci/build/github/FUSAKLA/prometheus-gitlab-notifier)](https://circleci.com/gh/FUSAKLA/prometheus-gitlab-notifier)
 [![GitHub tag (latest SemVer)](https://img.shields.io/github/tag/fusakla/prometheus-gitlab-notifier)](CHANGELOG.md)
 [![Docker Pulls](https://img.shields.io/docker/pulls/fusakla/prometheus-gitlab-notifier)](https://cloud.docker.com/repository/docker/fusakla/prometheus-gitlab-notifier)