Removing regexp anchors in routing constraints

They're not allowed according to [this](http://guides.rubyonrails.org/routing.html#segment-constraints) and this:
```
Regexp anchor characters are not allowed in routing requirements: /^(google|facebook)$/
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:137:in `verify_regexp_requirement'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:122:in `block in normalize_requirements!'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:120:in `each'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:120:in `normalize_requirements!'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:66:in `initialize'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:1443:in `new'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:1443:in `add_route'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:1422:in `decomposed_match'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:1403:in `block in match'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:1394:in `each'
/ruby-2.0.0-p353/gems/actionpack-4.0.1/lib/action_dispatch/routing/mapper.rb:1394:in `match'
```