rubygemsに登録するときにはspec.metadata['allowed_push_host']あたりを消しておこう ref: http://qiita.com/tossh/items/08e7165e730dbc1a0e2e

file0.txt

$ bundle exec rake release                           
sample_gem 0.1.0 built to pkg/sample_gem-0.1.0.gem.
Tag v0.1.0 has already been created.
rake aborted!
ERROR:  "https://rubygems.org" is not allowed by the gemspec, which only allows "TODO: Set to 'http://mygemserver.com'"
Pushing gem to https://rubygems.org...

Tasks: TOP => release => release:rubygem_push
(See full trace by running task with --trace)

file1.rb

# Prevent pushing this gem to RubyGems.org by setting 'allowed_push_host', or
# delete this section to allow pushing this gem to any host.$
if spec.respond_to?(:metadata)$
  spec.metadata['allowed_push_host'] = "TODO: Set to 'http://mygemserver.com'"
else
  raise "RubyGems 2.0 or newer is required to protect against public gem pushes."
end