Update .travis.yml

.travis.yml

@@ -1,5 +1,8 @@
 language: java
 sudo: false # faster builds
 
+jdk:
+  - oraclejdk8
+
 after_success:
-  - bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)