Garb bad request error "Invalid value 'ga:'. Values must match the following regular expression: '(-)?ga:.+'"

vigetlabs/garb#54

using mongoid

```ruby
linyows [master] ✝  bundle exec rails c
[1] 1.9.3(main)> Garb::Session.login(username, password)
[2] 1.9.3(main)> profile = Garb::Management::Profile.all.detect {|p| p.web_property_id == 'UA-XXXXXXX-X'}
[3] 1.9.3(main)> profile.exits(sort: :pageviews.desc)
Garb::BadRequestError: Invalid value 'ga:'. Values must match the following regular expression: '(-)?ga:.+'
from /var/www/app_name/vendor/bundle/ruby/1.9.1/bundler/gems/garb-72ce3c61ea8d/lib/garb/request/data.rb:59:in `handle_response'
```

The symbol-extension is conflicted.

```ruby
linyows [master] ✝  bundle exec pry
[1] 1.9.3(main)> :pageviews.desc
NoMethodError: undefined method `desc' for :pageviews:Symbol
from (pry):1:in `__pry__'
[2] 1.9.3(main)> require '/var/www/app_name/vendor/bundle/ruby/1.9.1/gems/origin-1.0.6/lib/origin'
=> true
[3] 1.9.3(main)> :pageviews.desc
=> #<Origin::Key:0x000000026f0a98
 @block=nil,
 @expanded=nil,
 @name=:pageviews,
 @operator=-1,
 @strategy=:__override__>
[4] 1.9.3(main)> require '/var/www/app_name/vendor/bundle/ruby/1.9.1/bundler/gems/garb-72ce3c61ea8d/lib/garb'
=> true
[5] 1.9.3(main)> :pageviews.desc
=> #<Origin::Key:0x000000027496c0
 @block=nil,
 @expanded=nil,
 @name=:pageviews,
 @operator=-1,
 @strategy=:__override__>
[6] 1.9.3(main)> exit
bye
linyows [master] ✝  bundle exec pry
[1] 1.9.3(main)> require '/var/www/app_name/vendor/bundle/ruby/1.9.1/bundler/gems/garb-72ce3c61ea8d/lib/garb'
=> true
[2] 1.9.3(main)> :pageviews.desc
=> #<SymbolOperator:0x00000001ebb6c0 @field=:pageviews, @operator=:desc>
[3] 1.9.3(main)> require '/var/www/app_name/vendor/bundle/ruby/1.9.1/gems/origin-1.0.6/lib/origin'
=> true
[4] 1.9.3(main)> :pageviews.desc
=> #<Origin::Key:0x00000001ec4b58
 @block=nil,
 @expanded=nil,
 @name=:pageviews,
 @operator=-1,
 @strategy=:__override__>
```