Removed deprecated bulk_threshold-instance method

http://www.rubydoc.info/github/rubygems/rubygems/Gem/ConfigFile#bulk_threshold-instance_method
Merge pull request #168 from jeffwidman/patch-1

Removed deprecated bulk_threshold-instance method
added npm completion
Merge commit 'e3a91cf78bd5f542f2fc1e3dbdc6fa450531c3d4'

* commit 'e3a91cf78bd5f542f2fc1e3dbdc6fa450531c3d4':
  Removed deprecated bulk_threshold-instance method