Configuring Chef provisioners fails if a proxy is set to false

[tmatilai]

The plugin errors out with e.g. config.proxy.http = false:

[default] Configuring proxy for Chef provisioners...
/Applications/Vagrant/embedded/lib/ruby/1.9.1/uri/common.rb:176:in `split': bad URI(is not URI?): false (URI::InvalidURIError)
    from /Applications/Vagrant/embedded/lib/ruby/1.9.1/uri/common.rb:211:in `parse'
    from /Applications/Vagrant/embedded/lib/ruby/1.9.1/uri/common.rb:747:in `parse'
    from /Users/tmatilai/.vagrant.d/gems/gems/vagrant-proxyconf-0.5.0/lib/vagrant-proxyconf/config/proxy.rb:54:in `user'
    from /Users/tmatilai/.vagrant.d/gems/gems/vagrant-proxyconf-0.5.0/lib/vagrant-proxyconf/config/proxy.rb:33:in `http_user'
    from /Users/tmatilai/.vagrant.d/gems/gems/vagrant-proxyconf-0.5.0/lib/vagrant-proxyconf/action/configure_chef_proxy.rb:57:in `configure_chef'

[tmatilai]

If someone is hitting this before the next release, the workaround is to use empty string "" instead of false.