Gemfile.lock not checked in - Heroku

While trying to "git push heroku master", I keep getting the error :

Counting objects: 266, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (239/239), done.
Writing objects: 100% (266/266), 222.68 KiB, done.
Total 266 (delta 55), reused 0 (delta 0)

-----> Heroku receiving push
-----> Rails app detected
-----> Detected Rails is not set to serve static_assets
       Installing rails3_serve_static_assets... done
-----> Gemfile detected, running Bundler version 1.0.3
       Unresolved dependencies detected; Installing...
       Using --without development:test
       You have modified your Gemfile in development but did not check
       the resulting snapshot (Gemfile.lock) into version control

       You have deleted from the Gemfile:
       * version: 1.0.6
       FAILED: http://docs.heroku.com/bundler
 !     Heroku push rejected, failed to install gems via Bundler

error: hooks/pre-receive exited with error code 1
To git@heroku.com:freezing-frost-65.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:freezing-frost-65.git'

I tried adding Gemfile and Gemfile.lock to git but to no avail. I tried removing .bundle directory and Gemfile.lock but the same error.