* ext/bigdecimal/bigdecimal.gemspec: Remove Gem::Specification#date
  We should rely on rubygems to create the date the gem was released
  for each version.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43841 b2dd03c8-39d4-4d8f-98ff-823fe69b080e