Fixes #2084 Sinatra tests fail due to missing mandatory headers Date and Server and inconsistent value in Content-Type header

frameworks/Ruby/sinatra/hello_world.rb

@@ -28,6 +28,12 @@ set :database, db_config.merge(:adapter => adapter, :host => ENV['DB_HOST'])
 settings.filters[:before].clear
 settings.filters[:after].clear
 
+after do
+  # Add mandatory HTTP headers to every response
+  response['Server'] ||= 'Puma'.freeze
+  response['Date'] ||= Time.now.to_s
+end
+
 class World < ActiveRecord::Base
   self.table_name = "World"
 end
@@ -41,7 +47,7 @@ get '/json' do
 end
 
 get '/plaintext' do
-  content_type 'text/plain'
+  response['Content-type'] = 'text/plain'
   'Hello, World!'
 end