I give up. No JDK 11 and JDK 7 travis support at the same time

I tried trusty, xenial and bionic. I tried to bundle jdk_switcher.

I tried different install_jdk.sh and jdk_switcher.sh. Either it
supports older versions or it supports newer versions. Some distros
don't have the scripts installed on Travis although the documentation
clearly states they do.

I just give up. I think right now it is more important that Travis
runs with older versions (java7) than newer because for end users
it is easier to install newer versions and test with them rather for
them to install older versions and test with those.

.travis.yml

@@ -8,7 +8,6 @@ jdk:
   - openjdk7
   - openjdk8
   - oraclejdk9
-  - openjdk11
 script:
   - jdk_switcher use $TRAVIS_JDK_VERSION
   - ./mvnw test -Dmaven.javadoc.skip=true