Copy updates and whitespace cleanup for services

- Bumped version from 3.5.0 to 3.5.1
- Updated hint text for YouTrack from http:// to https:// which is
  supported (but not enforced).
- Fixed a typo in the confirmation message for Github.
- Fixed whitespace in campfire, pagerduty, hipchat, sprintly, and some
  specs.

The key files with real changes are:

  lib/services/youtrack.rb
  lib/services/github.rb