travis: use jdk9 instead

Signed-off-by: Miguel Molina <[email protected]>
(cherry picked from commit 5881f6a)

Author: erizocosmico

.travis.yml

@@ -77,7 +77,7 @@ jobs:
         - make TEST=ruby integration
 
     - language: java
-      jdk: oraclejdk10
+      jdk: oraclejdk9
       before_install:
         - eval "$(gimme 1.11)"
       install: