Require YAML before using.

```
/usr/local/lib/ruby/gems/2.1.0/gems/asana-cli-0.0.2/bin/asana:34:in `block in <top (required)>': uninitialized constant YAML (NameError)
	from /usr/local/lib/ruby/gems/2.1.0/gems/asana-0.0.6/lib/asana/config.rb:14:in `configure'
	from /usr/local/lib/ruby/gems/2.1.0/gems/asana-cli-0.0.2/bin/asana:28:in `<top (required)>'
	from /usr/local/bin/asana:23:in `load'
	from /usr/local/bin/asana:23:in `<main>'
29891 glind ~/gits [git:master_]$ less /usr/local/lib/ruby/gems/2.1.0/gems/asana-0.0.6/lib/asana/config.rb
29892 glind ~/gits [git:master_]$ less ~/.asana_key
29893 glind ~/gits [git:master_]$ less /usr/local/lib/ruby/gems/2.1.0/gems/asana-cli-0.0.2/bin/asana:34
```