The trailing '/' isn't being picked up by Github anyway, and the link works as is.

actionpack/README.rdoc

@@ -322,7 +322,7 @@ The latest version of Action Pack 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/actionpack/
+* https://github.com/rails/rails/tree/master/actionpack
 
 
 == License

activemodel/README.rdoc

@@ -192,7 +192,7 @@ The latest version of Active Model 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/activemodel/
+* https://github.com/rails/rails/tree/master/activemodel
 
 
 == License

activeresource/README.rdoc

@@ -36,7 +36,7 @@ Putting Active Resource to use is very similar to Active Record.  It's as simple
 that inherits from ActiveResource::Base and providing a <tt>site</tt> class variable to it:
 
    class Person < ActiveResource::Base
-     self.site = "http://api.people.com:3000/"
+     self.site = "http://api.people.com:3000"
    end
 
 Now the Person class is REST enabled and can invoke REST services very similarly to how Active Record invokes

activesupport/README.rdoc

@@ -14,7 +14,7 @@ The latest version of Active Support 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/activesupport/
+* https://github.com/rails/rails/tree/master/activesupport
 
 
 == License