Fix graphite build for Gerrit v2.15

With I9797edde all the metrics reporter have been
built for v2.15. However, a typo was left in the graphite one
getting an inexistent branch.

This fixes the typo and resume a successful build
for the graphite plugin on v2.15

Change-Id: I0d0a17378500174dd3e4cdc5cf0cad6357f3fcd7
1 file changed
tree: 4d3c422640fdc14cb0ee0b8c12259f606d31a973
  1. jenkins/
  2. jenkins-docker/
  3. worker/
  4. .gitignore