ActiveSupport Message verifier now given an option to user to chooseto generate  url safe data

https://github.com/rails/rails/issues/14070

Fix this issue
We're using `ActiveSupport::MessageVerifier` to generate an auto-unsubscribe link. Something that we found awkward is that some tokens contains slash ('/') , this cause that unsubscribe route needs a globbing to work.

      u.unsubscription_token
      => "BAhpA/5gAQ==--ebb79a495452ba2bdc0335d45b921c238a19eccc"

       # http://.../unsubscribe/BAhpA/5gAQ==--ebb79a495452ba2bdc0335d45b921c238a19eccc

       # routes.rb
       get '/newsletter/unsubscribe/*signature' => 'newsletters#unsubscribe'

the slash is generated in message_verifier.rb#L47

        data = ::Base64.strict_encode64(Marshal.dump(90366))
          => "BAhpA/5gAQ=="

*now after fixing*
     
            data = ::Base64.strict_encode64(Marshal.dump(90366), url_safe: true)
          => ""BAhpA_5gAQ==""
     

so we are wondering shouldn't `ActiveSupport::MessageVerifier.new(secret_token).generate(user.id)` generate a token without slash? is ok if we add something to filter slash symbol in message_verifier.rb#L47 ???

cc @rafaelfranca  @NZKoz