fix alias_method order bug

alias_method's load order is wrong. 
As a result, bundle exec rake spec is failed....

```
/Users/u1/Repos/controller/vendor/bundle/ruby/2.1.0/gems/sidekiq-3.0.0/lib/sidekiq/testing.rb:59:in `alias_method': undefined method `raw_push' for class `Sidekiq::Client' (NameError)
	from /Users/u1/Repos/controller/vendor/bundle/ruby/2.1.0/gems/sidekiq-3.0.0/lib/sidekiq/testing.rb:59:in `<class:Client>'
	from /Users/u1/Repos/controller/vendor/bundle/ruby/2.1.0/gems/sidekiq-3.0.0/lib/sidekiq/testing.rb:58:in `<module:Sidekiq>'
	from /Users/u1/Repos/controller/vendor/bundle/ruby/2.1.0/gems/sidekiq-3.0.0/lib/sidekiq/testing.rb:3:in `<top (required)>'
	from /Users/u1/Repos/controller/vendor/bundle/ruby/2.1.0/gems/rspec-sidekiq-1.0.0/lib/rspec-sidekiq.rb:1:in `require'
	from /Users/u1/Repos/controller/vendor/bundle/ruby/2.1.0/gems/rspec-sidekiq-1.0.0/lib/rspec-sidekiq.rb:1:in `<top (required)>'
	from /Users/u1/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/bundler-1.6.1/lib/bundler/runtime.rb:76:in `require'
	from /Users/u1/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/bundler-1.6.1/lib/bundler/runtime.rb:76:in `block (2 levels) in require'
	from /Users/u1/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/bundler-1.6.1/lib/bundler/runtime.rb:72:in `each'
	from /Users/u1/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/bundler-1.6.1/lib/bundler/runtime.rb:72:in `block in require'
	from /Users/u1/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/bundler-1.6.1/lib/bundler/runtime.rb:61:in `each'
	from /Users/u1/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/bundler-1.6.1/lib/bundler/runtime.rb:61:in `require'
	from /Users/u1/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/bundler-1.6.1/lib/bundler.rb:132:in `require'
```