Drop deprecated (no replacement) method
diff --git a/lib/buildr/packaging/gems.rb b/lib/buildr/packaging/gems.rb
index da7bd06..241fff1 100644
--- a/lib/buildr/packaging/gems.rb
+++ b/lib/buildr/packaging/gems.rb
@@ -65,7 +65,6 @@
           spec.name = id
           spec.version = version.gsub('-','.') # RubyGems doesn't like '-' in version numbers
           spec.summary = full_comment
-          spec.has_rdoc = true
           spec.rdoc_options << '--title' << comment
           spec.require_path = 'lib'
         end