Run PolyGerrit UX tests with Java 8 only

Change-Id: Iba94f8bafe1a401a1166937bd02dd3bd38262cab
diff --git a/jenkins/gerrit-buck-test.sh b/jenkins/gerrit-buck-test.sh
index aab2c1e..c691157 100644
--- a/jenkins/gerrit-buck-test.sh
+++ b/jenkins/gerrit-buck-test.sh
@@ -25,8 +25,9 @@
     exit 0
   fi
 
-  echo 'PolyGerrit UX tests'
+  echo 'PolyGerrit UX tests (on Java8)'
   echo '----------------------------------------------'
+  . set-java.sh 8
   buck test --include web
 fi