Avoid issue with Bundler on Ruby 1.9

If you create a Gemfile with this content:

    gem "excecutor", git: 'git://github.com/benb/executor.git'

You'll get this exception:

Fetching git://github.com/benb/executor.git
remote: Counting objects: 17, done.
remote: Compressing objects: 100% (10/10), done.
remote: Total 17 (delta 5), reused 17 (delta 5)
Receiving objects: 100% (17/17), done.
Resolving deltas: 100% (5/5), done.
Unfortunately, a fatal error has occurred. Please report this error to the Bundler issue tracker at https://github.com/carlhuda/bundler/issues so that we can fix it. Thanks!
/home/rodrigo/.rvm/gems/ruby-1.9.3-p0/bundler/gems/executor-9fcc7493f4a0/executor.gemspec:8:in `block in <main>': uninitialized constant FileList (NameError)
        from /home/rodrigo/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems/specification.rb:1346:in `initialize'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/bundler/gems/executor-9fcc7493f4a0/executor.gemspec:1:in `new'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/bundler/gems/executor-9fcc7493f4a0/executor.gemspec:1:in `<main>'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler.rb:279:in `eval'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler.rb:279:in `rescue in block in load_gemspec'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler.rb:274:in `block in load_gemspec'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler.rb:272:in `chdir'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler.rb:272:in `load_gemspec'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/source.rb:340:in `block in load_spec_files'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/source.rb:339:in `each'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/source.rb:339:in `load_spec_files'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/source.rb:572:in `load_spec_files'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/source.rb:372:in `local_specs'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/source.rb:557:in `specs'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/definition.rb:430:in `block in converge_locked_specs'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/definition.rb:419:in `each'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/definition.rb:419:in `converge_locked_specs'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/definition.rb:180:in `resolve'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/definition.rb:127:in `specs'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/definition.rb:122:in `resolve_remotely!'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/installer.rb:48:in `run'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/installer.rb:12:in `install'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/cli.rb:220:in `install'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/vendor/thor/task.rb:22:in `run'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/vendor/thor/invocation.rb:118:in `invoke_task'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/vendor/thor.rb:263:in `dispatch'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/lib/bundler/vendor/thor/base.rb:386:in `start'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/gems/bundler-1.1.0/bin/bundle:13:in `<top (required)>'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/bin/bundle:19:in `load'
        from /home/rodrigo/.rvm/gems/ruby-1.9.3-p0/bin/bundle:19:in `<main>'