Fixing a small bug

Without this change I got nasty errors like this:

```>> EasyTranslate.detect("Hello")
NoMethodError: undefined method `delete' for nil:NilClass
	from /srv/apprentus/vendor/bundle/ruby/1.9.1/gems/easy_translate-0.3.2/lib/easy_translate/detection.rb:31:in `initialize'
	from /srv/apprentus/vendor/bundle/ruby/1.9.1/gems/easy_translate-0.3.2/lib/easy_translate/detection.rb:13:in `new'
	from /srv/apprentus/vendor/bundle/ruby/1.9.1/gems/easy_translate-0.3.2/lib/easy_translate/detection.rb:13:in `detect'
	from (irb):19
	from /srv/apprentus/vendor/bundle/ruby/1.9.1/gems/railties-3.2.11/lib/rails/commands/console.rb:47:in `start'
	from /srv/apprentus/vendor/bundle/ruby/1.9.1/gems/railties-3.2.11/lib/rails/commands/console.rb:8:in `start'
	from /srv/apprentus/vendor/bundle/ruby/1.9.1/gems/railties-3.2.11/lib/rails/commands.rb:41:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'```