Fix compatibility with newer rack versions

Author: andrehjr

lib/split/dashboard.rb

@@ -29,7 +29,8 @@ class Dashboard < Sinatra::Base
       if Object.const_defined?("Rails") && Rails.respond_to?(:env)
         @current_env = Rails.env.titlecase
       else
-        @current_env = "Rack: #{Rack.version}"
+        rack_version = Rack.respond_to?(:version) ? Rack.version : Rack.release
+        @current_env = "Rack: #{rack_version}"
       end
       erb :index
     end

lib/split/persistence/cookie_adapter.rb

@@ -47,8 +47,9 @@ def default_options
         end
 
         def set_cookie_via_rack(key, value)
-          delete_cookie_header!(@response.header, key, value)
-          Rack::Utils.set_cookie_header!(@response.header, key, value)
+          headers = @response.respond_to?(:header) ? @response.header : @response.headers
+          delete_cookie_header!(headers, key, value)
+          Rack::Utils.set_cookie_header!(headers, key, value)
         end
 
         # Use Rack::Utils#make_delete_cookie_header after Rack 2.0.0