fix vagrant synced folder mount options

This PR fixes access options for ```/vagrant``` folder. 

**Problem:** when I used VirtualBox 4.2.18 to set up environment I couldn't access shared folder ```/vagrant``` (I got permission denied error).
```
$ ls -la / | grep vagrant
d?????????   ? ?    ?        ?            ? vagrant
```

**Solution:** after I've updated ```Vagrantfile``` and ran ```vagrant up``` this problem was fixed
```
$ ls -la / | grep vagrant
drwxr-xr-x  1 vagrant vagrant  4096 Sep 19 14:50 vagrant
```