deleted sudo (#705)

Since travis has moved from a container-based environment to a VM-based
environment, there is no need to specify `sudo: false` anymore.

https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration
(cherry picked from commit cb4980b)

.travis.yml

@@ -10,7 +10,6 @@ matrix:
   include:
   - scala: 2.12.12
     jdk: openjdk11
-sudo: false
 cache:
   directories:
     - $HOME/.ivy2/cache