Removed trailing slash of 'Download and installation' Github URL as per convention

activerecord/README.rdoc

@@ -203,7 +203,7 @@ The latest version of Active Record can be installed with Rubygems:
 
 Source code can be downloaded as part of the Rails project on GitHub
 
-* https://github.com/rails/rails/tree/master/activerecord/
+* https://github.com/rails/rails/tree/master/activerecord
 
 
 == License