Fix Coveralls reports, now really tracks code coverage

Before, `Bundler.require` was executed before `Coveralls.wear!` was
called, therefore no actual code coverage was tracked. Instead
'invokations' of code within the spec folder was analyzed.

Also, now only Rubinius gets excluded from generating Coveralls reports,
MRI and JRuby work smoothly.
Add test case for invalid character in encoded UUID

Should raise an `Youyouaidi::InvalidUUIDError`