Add sudo false to builds

This builds on top of #79 (which hasn't been merged yet) and adds `sudo: false` as requested by @joshk.

I created PRs in the other projects from this:

* https://github.com/rspec/rspec-core/pull/1675
* https://github.com/rspec/rspec-expectations/pull/635
* https://github.com/rspec/rspec-mocks/pull/765
* https://github.com/rspec/rspec-rails/pull/1153
* https://github.com/rspec/rspec-support/pull/104