* Only include simplecov gem on MRI 2.1
* Only include coveralls gem on MRI 2.1
* Remove rubinius-developer_tools, which is no longer needed since we
are not running coveralls on rubinius
* Do not try to require coveralls on rubinius (`platform :mri_21`
includes rbx, so we need to check if Rubinius is defined)
They're only needed when generating docs, so no need to load them all
the time. This also lets us more easily test situations where the Maruku
filter is not defined or its dependencies are unavailable.
I recently added a rescue from LoadError if the Maruku and Textile
filters from haml-contrib aren't available. Since we don't test those
filters here, there's no longer any need to depend on haml-contrib even
for development.
See issue #551
[ci skip]
