Use JDK 11 in Travis builds

Author: DamianDunajski

.travis.yml

@@ -1,7 +1,8 @@
+dist: xenial
 sudo: required
 language: java
 jdk:
-  - oraclejdk8
+  - openjdk11
 before_cache:
   - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
   - rm -fr $HOME/.gradle/caches/*/plugin-resolution/