manifest: Point the kokoro build dir to the master branch

Change-Id: I0fd5e0ebec4f2a04c0e834f86ad59d81cc391b52
diff --git a/enterprise.xml b/enterprise.xml
index 52fc4c3..40822b4 100644
--- a/enterprise.xml
+++ b/enterprise.xml
@@ -87,6 +87,6 @@
       groups="notdefault,internal" remote="coral-internal" />
 
     <project name="kokoro-enterprise" path="kokoro"
-      groups="notdefault,internal" remote="coral-internal" />
+      groups="notdefault,internal" remote="coral-internal" revision="master" />
     <!-- END closed source repositories -->
 </manifest>