Build the saml plugin on master

Saml plugin currently does not have stable-2.16 and other branches and
does not need those branches yet.

Change-Id: I913e7ba418c9a76c01cd39ccf0d0da24c4bcff0a
diff --git a/jenkins/gerrit-plugin-saml.yaml b/jenkins/gerrit-plugin-saml.yaml
index 687c6c5..449655a 100644
--- a/jenkins/gerrit-plugin-saml.yaml
+++ b/jenkins/gerrit-plugin-saml.yaml
@@ -3,6 +3,7 @@
     jobs:
       - 'plugin-{name}-bazel-{branch}':
           branch:
+            - master
             - stable-2.15
             - stable-2.14
       - 'plugin-{name}-sbt-{branch}':