Coveralls#wear! changed to use 'rails' config

According to https://coveralls.io/docs/ruby, rails projects
have to call `Coveralls.wear!('rails') instead of Coverall.wear!

Also, Coveralls has to be required and 'worn' first in the
`test_helper.rb` otherwise it won't report accurate numbers.

This teeny fix should make the coverage numbers more accurate, and
prevent actual test files from being listed in the coverage report.