Update travis

Author: emmanuel-keller

.travis.yml

@@ -1,16 +1,11 @@
 language: java
 jdk:
-  - oraclejdk8
-  - oraclejdk9
+  - openjdk11
 sudo: false
 cache:
   directories:
   - $HOME/.m2
-addons:
-  apt:
-    packages:
-      - oracle-java8-installer
-      - oracle-java9-installer
+
 install: mvn install -DskipTests=true -Dgpg.skip=true -Dmaven.javadoc.skip=true -B -V -U
 after_success:
   - mvn clean test jacoco:report coveralls:report