Ignore stories without an estimate when delivering.

Without this, `cap deploy` would fail with the following output

    * delivering tracker stories ...
    /Users/jakob/.rvm/gems/ruby-1.9.3-p194@bundler/gems/deploy_and_deliver-2.1.2/lib/deploy_and_deliver.rb:17:in `+': nil can't be coerced into Fixnum (TypeError)
      from /Users/jakob/.rvm/gems/ruby-1.9.3-p194@bundler/gems/deploy_and_deliver-2.1.2/lib/deploy_and_deliver.rb:17:in `each'
      from /Users/jakob/.rvm/gems/ruby-1.9.3-p194@bundler/gems/deploy_and_deliver-2.1.2/lib/deploy_and_deliver.rb:17:in `inject'
      from /Users/jakob/.rvm/gems/ruby-1.9.3-p194@bundler/gems/deploy_and_deliver-2.1.2/lib/deploy_and_deliver.rb:17:in `deliver_and_report'
      from /Users/jakob/.rvm/gems/ruby-1.9.3-p194@bundler/gems/deploy_and_deliver-2.1.2/lib/deploy_and_deliver/recipes.rb:12:in `block (3 levels) in <top (required)>'
    [...]

if a delivered story happened to not have an estimate.
Merge pull request #3 from koppen/fix_delivery_of_stories_with_no_estimate

Fix delivery of stories with no estimate