Require guard

Fixes error:

/usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/guard-rspec-4.4.1/lib/guard/rspec/options.rb:6:in `<module:Guard>': uninitialized constant Guard::Plugin (NameError)
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/guard-rspec-4.4.1/lib/guard/rspec/options.rb:5:in `<top (required)>'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/guard-rspec-4.4.1/lib/guard/rspec.rb:1:in `<top (required)>'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/bundler-1.7.7/lib/bundler/runtime.rb:85:in `require'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/bundler-1.7.7/lib/bundler/runtime.rb:85:in `rescue in block in require'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/bundler-1.7.7/lib/bundler/runtime.rb:68:in `block in require'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/bundler-1.7.7/lib/bundler/runtime.rb:61:in `each'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/bundler-1.7.7/lib/bundler/runtime.rb:61:in `require'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/bundler-1.7.7/lib/bundler.rb:133:in `require'
	from /Users/penman/projects/you_rock/config/application.rb:14:in `<top (required)>'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/railties-4.2.0.rc2/lib/rails/commands/commands_tasks.rb:78:in `require'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/railties-4.2.0.rc2/lib/rails/commands/commands_tasks.rb:78:in `block in server'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/railties-4.2.0.rc2/lib/rails/commands/commands_tasks.rb:75:in `tap'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/railties-4.2.0.rc2/lib/rails/commands/commands_tasks.rb:75:in `server'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/railties-4.2.0.rc2/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/railties-4.2.0.rc2/lib/rails/commands.rb:17:in `<top (required)>'
	from /Users/penman/projects/you_rock/bin/rails:8:in `require'
	from /Users/penman/projects/you_rock/bin/rails:8:in `<top (required)>'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/spring-1.2.0/lib/spring/client/rails.rb:27:in `load'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/spring-1.2.0/lib/spring/client/rails.rb:27:in `call'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/spring-1.2.0/lib/spring/client/command.rb:7:in `call'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/spring-1.2.0/lib/spring/client.rb:26:in `run'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/spring-1.2.0/bin/spring:48:in `<top (required)>'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/spring-1.2.0/lib/spring/binstub.rb:11:in `load'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/gems/spring-1.2.0/lib/spring/binstub.rb:11:in `<top (required)>'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from /usr/local/var/rbenv/versions/2.1.2/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
	from /Users/penman/projects/you_rock/bin/spring:16:in `<top (required)>'
	from bin/rails:3:in `load'
	from bin/rails:3:in `<main>'