Change regexp anchors to fix security risk error thrown by activemodel

It seems activemodel's latest versions doesn't accept multiline anchors without providing an option.

I ran into this error when trying to load the environment:

```bash
/Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/format.rb:46:in `check_options_validity': The provided regular expression is using multiline anchors (^ or $), which may present a security risk. Did you mean to use \A and \z, or forgot to add the :multiline => true option? (ArgumentError)
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/format.rb:20:in `check_validity!'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validator.rb:143:in `initialize'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/with.rb:87:in `new'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/with.rb:87:in `block in validates_with'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/with.rb:86:in `each'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/with.rb:86:in `validates_with'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/validates.rb:119:in `block in validates'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/validates.rb:109:in `each'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activemodel-4.0.2/lib/active_model/validations/validates.rb:109:in `validates'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/braspag-pagador-1.0.0/lib/braspag-pagador/core/order.rb:67:in `block in <class:Order>'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/braspag-pagador-1.0.0/lib/braspag-pagador/core/order.rb:64:in `each'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/braspag-pagador-1.0.0/lib/braspag-pagador/core/order.rb:64:in `<class:Order>'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/braspag-pagador-1.0.0/lib/braspag-pagador/core/order.rb:30:in `<module:BraspagPagador>'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/braspag-pagador-1.0.0/lib/braspag-pagador/core/order.rb:1:in `<top (required)>'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `block in require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:214:in `load_dependency'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/braspag-pagador-1.0.0/lib/braspag-pagador.rb:17:in `<top (required)>'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353@global/gems/bundler-1.5.0.rc.1/lib/bundler/runtime.rb:76:in `require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353@global/gems/bundler-1.5.0.rc.1/lib/bundler/runtime.rb:76:in `block (2 levels) in require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353@global/gems/bundler-1.5.0.rc.1/lib/bundler/runtime.rb:72:in `each'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353@global/gems/bundler-1.5.0.rc.1/lib/bundler/runtime.rb:72:in `block in require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353@global/gems/bundler-1.5.0.rc.1/lib/bundler/runtime.rb:61:in `each'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353@global/gems/bundler-1.5.0.rc.1/lib/bundler/runtime.rb:61:in `require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353@global/gems/bundler-1.5.0.rc.1/lib/bundler.rb:131:in `require'
	from /Users/mateus/Code/codeminer42/diagnostycos/config/application.rb:12:in `<top (required)>'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.0.2/lib/rails/commands.rb:43:in `require'
	from /Users/mateus/.rvm/gems/ruby-2.0.0-p353/gems/railties-4.0.2/lib/rails/commands.rb:43:in `<top (required)>'
	from bin/rails:4:in `require'
	from bin/rails:4:in `<main>'
```