Update quickstart.md

I've noticed that it seems the "--name" tag is no longer supported by the vagrant command line.

Here is the error that I received:

trammell@trammell-pcu:~$ vagrant box add http://gigaspaces-repository-eu.s3.amazonaws.com/org/cloudify3/3.0.0/nightly_6/cloudify_3.0.0_virtualbox.box --name=cloudify
An invalid option was specified. The help for this command
is available below.

Usage: vagrant box add <name> <url> [--provider provider] [-h]

        --checksum VALUE             Checksum
        --checksum-type VALUE        Checksum type
    -c, --clean                      Remove old temporary download if it exists.
    -f, --force                      Overwrite an existing box if it exists.
        --insecure                   If set, SSL certs will not be validated.
        --cacert certfile            CA certificate
        --cert certfile              The client SSL cert
        --provider provider          The provider that backs the box.
    -h, --help                       Print this help

trammell@trammell-pcu:~$ vagrant box add cloudify /media/trammell/HRM_CCSA_X6/cloudify_3.1.0-rc1_virtualbox.box 
Downloading box from URL: file:/media/trammell/HRM_CCSA_X6/cloudify_3.1.0-rc1_virtualbox.box
Extracting box...te: 25.4M/s, Estimated time remaining: --:--:--)
Successfully added box 'cloudify' with provider 'virtualbox'!