Because i have a error without this dependency.
```
$ rspec spec
/Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/em-http-request-1.0.3/lib/em-http/middleware/json_response.rb:1:in `require': cannot load such file -- yajl (LoadError)
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/em-http-request-1.0.3/lib/em-http/middleware/json_response.rb:1:in `<top (required)>'
        from /Users/8xx8/projects/tweetstream/lib/tweetstream/site_stream_client.rb:3:in `require'
        from /Users/8xx8/projects/tweetstream/lib/tweetstream/site_stream_client.rb:3:in `<top (required)>'
        from /Users/8xx8/projects/tweetstream/spec/tweetstream/site_stream_client_spec.rb:3:in `<top (required)>'
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/rspec-core-2.14.7/lib/rspec/core/configuration.rb:896:in `load'
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/rspec-core-2.14.7/lib/rspec/core/configuration.rb:896:in `block in load_spec_files'
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/rspec-core-2.14.7/lib/rspec/core/configuration.rb:896:in `each'
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/rspec-core-2.14.7/lib/rspec/core/configuration.rb:896:in `load_spec_files'
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/rspec-core-2.14.7/lib/rspec/core/command_line.rb:22:in `run'
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/rspec-core-2.14.7/lib/rspec/core/runner.rb:80:in `run'
        from /Users/8xx8/.rvm/gems/ruby-1.9.3-p448/gems/rspec-core-2.14.7/lib/rspec/core/runner.rb:17:in `block in autorun'
Coverage report generated for RSpec to /Users/8xx8/projects/tweetstream/coverage. 232 / 839 LOC (27.65%) covered.
```