Tag master build as 'latest'. (#66)

diff --git a/.travis.yml b/.travis.yml
index 78ebd23..2a2c1db 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -29,7 +29,7 @@
       all_branches: true
       repo: apache/incubator-openwhisk-runtime-java
   - provider: script
-    script: "./tools/travis/publish.sh openwhisk 8 master"
+    script: "./tools/travis/publish.sh openwhisk 8 latest"
     on:
       branch: master
       repo: apache/incubator-openwhisk-runtime-java