Fix synced folders for Vagrant 1.2.x.

On Vagrant 1.2.x, using the latest stable version of VVV, `vagrant up` returns the following error:

```
[default] -- /srv/www
The following SSH command responded with a non-zero exit status.
Vagrant assumes that this means the command failed!

mount -t vboxsf -o uid=`id -u www-data`,gid=`id -g vagrant`,["dmode=775", "fmode
=774"] /srv/www /srv/www
```

I get it to work by modifying the block between lines 106 and 110:

```
  if vagrant_version >= "1.3.0"
    config.vm.synced_folder "www/", "/srv/www/", :owner => "www-data", :mount_options => [ "dmode=775", "fmode=774" ]
  else
    config.vm.synced_folder "www/", "/srv/www/", :owner => "www-data", :extra => [ "dmode=775", "fmode=774" ]
  end
```

With this:

```
  if vagrant_version >= "1.3.0"
    config.vm.synced_folder "www/", "/srv/www/", :owner => "www-data", :mount_options => [ "dmode=775", "fmode=774" ]
  else
    config.vm.synced_folder "www/", "/srv/www/", :owner => "www-data", :extra => 'dmode=775,fmode=774'
  end
```

I think that this should be modified to work with 1.2.x versions. I also found this Stackoverflow topic: http://stackoverflow.com/questions/13169154/cannot-change-permissions-of-folders-within-vagrant-home-folder, where this guy comments on how the format  for mount options changed across versions.