travis: Remove oracle JDKs from config

This time, oraclejdk10 fails with a "oraclejdk10 is deprecated." message.  It's just going to get worse over time and isn't worth the effort to maintain on travis.

.travis.yml

@@ -6,22 +6,13 @@ install: true
 
 matrix:
   include:
-# 7
     - jdk: openjdk7
       env: GRADLE_OPTS="-Xmx386m -Xms386m -XX:MaxPermSize=128m" # Java 7 still uses separate permgen
       before_script: # Workaround for https://github.com/travis-ci/travis-ci/issues/8503
         - sudo sed -i 's/security.provider.9/#security.provider.9/g' $JAVA_HOME/jre/lib/security/java.security
-# 8
-    - jdk: oraclejdk8
     - jdk: openjdk8
-# 9
-    - jdk: oraclejdk9
     - jdk: openjdk9
-# 10
-    - jdk: oraclejdk10
     - jdk: openjdk10
-# 11
-    - jdk: oraclejdk11
     - jdk: openjdk11
 
 env: