Update TravisCI setting to new vm based builds

[abelsromero]

As mentioned here: https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration

Travis is disabling docker model.
This PR just removes configurations that not necessary or working:

• removes sudo: false
• removes dist: trusty, which is not needed since trusty is already default

[coveralls]

Coverage remained the same at 69.101% when pulling 1a0e03e on abelsromero:update_travis_to_new_vm_based_build into c749461 on asciidoctor:master.

[coveralls]

Coverage remained the same at 69.101% when pulling 3705223 on abelsromero:update_travis_to_new_vm_based_build into c749461 on asciidoctor:master.

[mojavelinux]

I think we should still leave the dist line. While trusty may be the default today, when it becomes not the default, then we could run into a problem. Including it also increases transparency about what the build is actually using.

[abelsromero]

restored

[mojavelinux]

👍

Btw, if Travis gives other advice about how to use the dist field, then of course we can follow it. Let's keep an eye out for that advice.