Q:

Heroku, Zentest, Rails 3 - error while pushing

I am trying to push to heroku by git push heroku master.
And I have this error.
 Fetching source index for http://rubygems.org/
       Installing rake (0.9.2.2) 
       Installing ZenTest (4.6.2) /usr/ruby1.9.2/lib/ruby/1.9.1/rubygems/installer.rb:170:in `install': ZenTest requires RubyGems version ~> 1.8. Try 'gem update --system' to update RubyGems itself. (Gem::InstallError)

But I do not need ZenTest at all. I deleted this gem from my gemfile.
Now my gemfile looks like this 
source 'http://rubygems.org'

gem 'rails', '3.1.1'
gem 'sqlite3'
gem 'jquery-rails'
gem "rmagick"
gem "carrierwave"

#gem 'compass_twitter_bootstrap'
#gem 'gravatar_image_tag', '1.0.0.pre2'

group :development do
  #gem 'rspec-rails', '2.6.1'
  #gem 'annotate', '2.4.0' 
end

group :test do
  #gem 'rspec-rails', '2.6.1'
  #gem 'webrat', '0.7.1'
   gem 'turn', :require => false 

end

group :assets do
  gem 'sass-rails',   '~> 3.1.4'
  gem 'coffee-rails', '~> 3.1.1'
  gem 'uglifier', '>= 1.0.3'
  gem 'twitter-bootstrap-rails'

end

source :gemcutter
    gem 'sinatra', '1.0'

Then i run rvmsudo bundle to delete it from gemfile.lock.
But i still have this error. 
What can do with this?

A:

Did you do a git commit after modifying the gemfile?

