Revert "Simplify .travis.yml definition"
Revert "Simplify .travis.yml definition"

This reverts commit 0b26255e2ab726efea67e210e57a491dad6ca8eb.

It somehow didn't work...
https://travis-ci.org/ruby-bench/ruby-bench-docker/builds/401338865

ruby-bench/ruby-bench-docker,ruby-bench/ruby-bench-docker