Remove oraclejdk7 from travis configuration, because it is no longer available.

PascalSchumacher · PascalSchumacher · commit 253bc8f14abf · 2017-07-28T18:41:53.000+02:00
see: travis-ci/travis-ci#7964 (comment) for details
diff --git a/.travis.yml b/.travis.yml
@@ -18,7 +18,6 @@ sudo: false
 
 jdk:
   - openjdk7
-  - oraclejdk7
   - oraclejdk8
 
 after_success:
