To not run the tests on ruby 2.0 because it hit EOL

Official support for ruby 2.0 ended in february: https://www.ruby-lang.org/en/news/2016/02/24/support-plan-of-ruby-2-0-0-and-2-1/

.travis.yml

@@ -25,7 +25,6 @@ matrix:
     - rvm: 2.3.0
       env: DATABASE_ADAPTER=mysql2 DOCKER_IMAGE=cantino/huginn DOCKERFILE=docker/multi-process/Dockerfile
 rvm:
-- 2.0.0
 - 2.1
 - 2.2
 - 2.3.0