Turns out JDK8 is no longer supported on Travis CI.

pramodsu · pramodsu · commit 4ddcdd3f82c1 · 2019-12-07T11:59:25.000+05:30
diff --git a/.travis.yml b/.travis.yml
@@ -2,7 +2,6 @@ language: scala
 scala:
     - 2.12.7
 jdk:
-    - oraclejdk8
     - oraclejdk11
 cache:
   directories:
