Fix gem homepage

paperclip.gemspec

@@ -13,7 +13,7 @@ spec = Gem::Specification.new do |s|
   s.version           = Paperclip::VERSION
   s.author            = "Jon Yurek"
   s.email             = "jyurek@thoughtbot.com"
-  s.homepage          = "http://www.thoughtbot.com/projects/paperclip"
+  s.homepage          = "https://github.com/thoughtbot/paperclip"
   s.description       = "Easy upload management for ActiveRecord"
   s.platform          = Gem::Platform::RUBY
   s.summary           = "File attachments as attributes for ActiveRecord"