Fixing gem grouping and simplecov version

This fixes two warnings/errors:

The latest simplecov is not working properly (see colszowka/simplecov#281), and it calls `exit` within a `Kernel.at_exit`, which causes irb to explode on exit.

With fuubar in the development group, this warning is logged on irb start, because fuubar requires rspec:
`irb: warn: can't alias context from irb_context.`

On a related note, should more of the gems in the :development/:test combined group be moved to only test? For example, I see jasminerice routes in `rake routes`