Build `its-phabricator` master branch

`its-base` builds fine again on master, so we can add `its-phabricator`
on master too.

Change-Id: Ibd49c50292c62bbee9a84d2f3d524c57c21ce5c4
diff --git a/jenkins/gerrit-bazel-plugin-its-phabricator.yaml b/jenkins/gerrit-bazel-plugin-its-phabricator.yaml
index 7730926..009bcb6 100644
--- a/jenkins/gerrit-bazel-plugin-its-phabricator.yaml
+++ b/jenkins/gerrit-bazel-plugin-its-phabricator.yaml
@@ -3,6 +3,7 @@
     jobs:
       - 'plugin-its-{name}-bazel-{branch}':
           branch:
+            - master
             - stable-3.2
             - stable-3.1
             - stable-3.0