Fix syntax in requirements
Fix syntax in requirements

chrisroberts/vagrant-installers,chrisroberts/vagrant-installers,chrisroberts/vagrant-installers,chrisroberts/vagrant-installers,mitchellh/vagrant-installers,mitchellh/vagrant-installers,chrisroberts/vagrant-installers,mitchellh/vagrant-installers,mitchellh/vagrant-installers,chrisroberts/vagrant-installers,mitchellh/vagrant-installers,mitchellh/vagrant-installers