Vagrantfile compatibility fix with ruby v1.8

    > vagrant up
    
    There is a syntax error in the following Vagrantfile. The syntax error
    message is reproduced below for convenience:

    /path_to_kuma/Vagrantfile:58: syntax error, unexpected ':', expecting kEND
        config.vm.synced_folder ".", "/vagrant", disabled:  true
                                                      ^