Use RSpec 2.x until Travis/Capybara issues resolve

https://travis-ci.org/thoughtbot/suspenders/builds/26602519

    rspec-support-3.0.0/lib/rspec/support/version_checker.rb:28:in
    `raise_too_low_error': You are using capybara 2.1.0. RSpec requires
    version >= 2.2.0. (RSpec::Support::LibraryVersionTooLowError)

https://rubygems.org/gems/capybara-webkit
Remove SimpleCov

* SimpleCov was returning zero status even when build failed.
* Remove SimpleCov so that we get real build results on Travis.
* The team was reporting not regularly reviewing the coverage stats.