Remove sidekiq-spy mailing list from build notifications.

This doesn't work, as Travis CI can't confirm the mailing list
subscription. But perhaps it's best not to flood the mailing list with
build notifications, anyway. If you'd like to be notified of builds,
however, please add your address and send a pull request. :)
Tweak build list, sorting order.
Revert "Configure https://coveralls.io, installing coveralls ."

This reverts commit f5af9fa47b143effd75ed16a857ff057c77e3508.

Conflicts:
	README.md
Fix test Spy::Stats undefined Minitest.

It's `MiniTest`. Ruby 2.0.0 allows `Minitest` which returns `MiniTest`;
Ruby 1.9.3 does not.
Allow class overrides in Spy::Stats#initialize .

This allows for external instances to be used instead of creating new
ones. It also makes testing easier.
Change Spy::Stats test to not use stubs on classes.

Although using stubs on classes works in Ruby 2.0.0, Ruby 1.9.3 errors
with it not being defined. Utilise the class overrides available in
`Spy::Stats`, and override selected Redis methods by mixing in modules
within tests.
Revert "Allow build failures for Ruby 1.9.3 ."

This reverts commit c2aedf13ed46282411a1d44ad8a944acae1c725e.
Merge branch 'ruby-1.9.3-fixes' into develop