[GRIFFIN-299] Add oracle jdk8 support in travis build phase

As Ubuntu Xenial has become the default Travis CI build environment, we may build fail. 

The workaround is to either add `dist: trusty` to your .travis.yml file or use `openjdk8`.

Author: wankunde <wankunde@163.com>

Closes #552 from wankunde/travis.
diff --git a/.travis.yml b/.travis.yml
index 68705ab..319902c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,6 @@
 # or implied. See the License for the specific language governing permissions and limitations under
 # the License.
 
-
 language: java scala node_js
 
 services:
@@ -20,9 +19,8 @@
 env:
   - COMPOSE_FILE=griffin-doc/docker/compose/docker-compose-batch.yml
 
-
 jdk:
-  - oraclejdk8
+  - openjdk8
 scala:
   - 2.10.6
 node_js: