Add JDK11 to the Travis config.

Sean Sullivan · cgdecker · commit 3912da1f70af · 2018-09-28T14:46:13.000-04:00
Closes google#3274 RELNOTES=n/a ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=214450758
diff --git a/.travis.yml b/.travis.yml
@@ -5,6 +5,7 @@ language: java
 jdk:
   - oraclejdk8
   - oraclejdk10
+  - openjdk11
 
 # https://github.com/travis-ci/travis-ci/issues/3259#issuecomment-130860338
 addons:
