Remove deprecated rubyforge_project attribute from gemspec.

Proof: http://rubygems.rubyforge.org/rubygems-update/Gem/Specification.html#attribute-i-rubyforge_project

Author: hedgesky

grape.gemspec

@@ -12,8 +12,6 @@ Gem::Specification.new do |s|
   s.description = 'A Ruby framework for rapid API development with great conventions.'
   s.license     = 'MIT'
 
-  s.rubyforge_project = 'grape'
-
   s.add_runtime_dependency 'rack', '>= 1.3.0'
   s.add_runtime_dependency 'rack-mount'
   s.add_runtime_dependency 'rack-accept'