Changing oraclejdk8 to openjdk8 in hopes that it will fix our Travis builds.

netdpb · cpovirk · commit 05df9d3b5c10 · 2019-08-19T14:57:31.000-04:00
------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=263837785
diff --git a/.travis.yml b/.travis.yml
@@ -8,7 +8,7 @@ notifications:
     on_failure: always
 
 jdk:
-  - oraclejdk8
+  - openjdk8
   - openjdk9
   - openjdk10
   - openjdk11
