Remove rubyforge reference.

Author: gkellogg

json-ld.gemspec

@@ -10,7 +10,6 @@ Gem::Specification.new do |gem|
   gem.license               = 'Unlicense'
   gem.summary               = "JSON-LD reader/writer for Ruby."
   gem.description           = "JSON::LD parses and serializes JSON-LD into RDF and implements expansion, compaction and framing API interfaces."
-  gem.rubyforge_project     = 'json-ld'
 
   gem.authors               = ['Gregg Kellogg']
   gem.email                 = 'public-linked-json@w3.org'