Change install task

See https://github.com/travis-ci/travis-ci/issues/2821 for details, issues with parralel and rbx
Fix indentation
Merge pull request #78 from petems/patch-1

Change install task
Add simplecov to development dependancies
Basic setup to enable simplecov
Ignore coverage/* folder

Otherwise you end up with a load of HTML and JS in VCS! :dancer:
Pending spec file for `GoCardless::Error` class