Use https:// instead of git:// for README URLs

See #2327.

git:// URLs are insecure and cause recent versions of Bundler to emit a
warning.

Author: alyssais

README.md

@@ -15,7 +15,7 @@ RSpec repos as well. Add the following to your `Gemfile`:
 
 ```ruby
 %w[rspec rspec-core rspec-expectations rspec-mocks rspec-support].each do |lib|
-  gem lib, :git => "git://github.com/rspec/#{lib}.git", :branch => 'master'
+  gem lib, :git => "https://github.com/rspec/#{lib}.git", :branch => 'master'
 end
 ```