Fix reference to native Logger in Marmot::Client

I got this error when using marmot:

```
/Library/Ruby/Gems/2.0.0/gems/marmot-0.0.5/lib/marmot/client.rb:15:in `initialize': undefined method `new' for HTTParty::Logger:Module (NoMethodError)
	from /Library/Ruby/Gems/2.0.0/gems/marmot-0.0.5/bin/marmot:116:in `new'
	from /Library/Ruby/Gems/2.0.0/gems/marmot-0.0.5/bin/marmot:116:in `start'
	from /Library/Ruby/Gems/2.0.0/gems/marmot-0.0.5/bin/marmot:125:in `<top (required)>'
	from /usr/bin/marmot:23:in `load'
	from /usr/bin/marmot:23:in `<main>'
```

It seems that's because HTTParty added a `Logger` class of its own.