Use oraclejdk11 in Travis build

JDK 8 is no longer supported for sonarqube analysis, see:
https://travis-ci.org/github/metafacture/metafacture-core/builds/764392244#L1514

Author: fsteeg

.travis.yml

@@ -18,7 +18,7 @@ sudo: false
 dist: trusty
 language: java
 jdk:
-  - oraclejdk8
+  - oraclejdk11
 addons:
   sonarcloud:
     organization: metafacture