THRIFT-486. rb: ruby tutorial needs updated require statements

Fixed. 



git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@771969 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/tutorial/rb/RubyServer.rb b/tutorial/rb/RubyServer.rb
index 89eb373..30aa7f2 100755
--- a/tutorial/rb/RubyServer.rb
+++ b/tutorial/rb/RubyServer.rb
@@ -24,7 +24,7 @@
 
 require 'thrift'
 
-require 'Calculator'
+require 'calculator'
 require 'shared_types'
 
 class CalculatorHandler