OpenJDK 10 is EOL and no longer supported by Travis-CI.

See https://docs.travis-ci.com/user/languages/java/#using-java-10-and-later
"Take note that oraclejdk10 is EOL since October 2018 and as such it’s
not supported anymore on Travis CI. See
https://www.oracle.com/technetwork/java/javase/eol-135779.html."
diff --git a/.travis.yml b/.travis.yml
index 630e6b4..6f9d5e7 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -24,7 +24,6 @@
 jdk:
   - oraclejdk11
   - openjdk8
-  - openjdk10
   - openjdk11
   - openjdk12
   - openjdk13