wraith should not be requiring bundler

On a clean build of ruby, after a fresh install of wraith:

```
$ wraith 
/Users/jasonkarns/.rbenv/versions/2.0.0-p353/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:53:in `require': cannot load such file -- bundler/setup (LoadError)
	from /Users/jasonkarns/.rbenv/versions/2.0.0-p353/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:53:in `require'
	from /Users/jasonkarns/.rbenv/versions/2.0.0-p353/lib/ruby/gems/2.0.0/gems/wraith-1.1.4/bin/wraith:3:in `<top (required)>'
	from /Users/jasonkarns/.rbenv/versions/2.0.0-p353/bin/wraith:23:in `load'
	from /Users/jasonkarns/.rbenv/versions/2.0.0-p353/bin/wraith:23:in `<main>'
```

Wraith doesn't depend on bundler and shouldn't be requiring it.