Fix Travis integration config option in .coveralls.yml.

"Another important option is service_name which allows you to specify where Coveralls should look to find additional information about your builds. This can be any string, but using travis-ci or travis-pro will allow Coveralls to fetch branch data, comment on pull requests, and more."
Add CONTRIBUTING.md
Add MIT license.
implement user role
implement role in instance_user
test cases for user role & refine exsiting tests
set role in factories
tests for instance role(pending)
comment out enum field and use numbers for now
add spaces after # as hound suggested
update schema validations gem
update user model specs
reorder role columns in schema file
course model specs
implement course model according to specs
enrolment specs
implement enrolment model
enrolment role specs
course user relations through enrolment
Add inverse_of to both user and course model