depending on bcrypt gem (not bcrypt-ruby)

Conflicts:
	gemfiles/Gemfile.rails-4.1-stable
Travis configuration update

- use system libraries to build Nokogiri
- test with Ruby 1.9.3 and 2.1.x
- don't test Rails-head with Ruby 1.9.3
Rails 4.2 compatibility
depending on bcrypt gem (not bcrypt-ruby)