Move Travis to openjdk11, oraclejdk11 does not work anymore

Author: Enrico Olivelli <eolivelli@apache.org>

Reviewers: Norbert Kalmar <nkalmar@apache.org>

Closes #1005 from eolivelli/fix/travis-openjdk11

.travis.yml

@@ -2,7 +2,7 @@ language: java
 sudo: false
 jdk:
   - openjdk8
-  - oraclejdk11
+  - openjdk11
 
 cache:
   directories: