Trigger Jenkins test jobs for '2018.8.1' branch of formulas as well

Change-Id: I9bb93142b755a0c3bb4dfab9cb62f792ee3c4e01
diff --git a/jenkins/client/job/salt-formulas/tests.yml b/jenkins/client/job/salt-formulas/tests.yml
index ca8d0a5..b5b286d 100644
--- a/jenkins/client/job/salt-formulas/tests.yml
+++ b/jenkins/client/job/salt-formulas/tests.yml
@@ -153,6 +153,7 @@
                   salt-formulas/{{name}}:
                     branches:
                       - master
+                      - '2018.8.1'
                 event:
                   comment:
                     - addedContains: