The MISSING shields.io badge, Jenkins-coverage.
This tiny web server will generate your Jenkins-code-coverage badge!
# install
$ npm install -g jenkins-coverage-badge
# run with port number (default: 9913)
$ jcb 80
Listening on port 80...
Now you can get coverage badge with,
http://host:port/jenkins/c/http/:jenkins_url/job/:job

MIT