updated opam version to 1.2 from 1.1.1;
updated opam version to 1.2 from 1.1.1;

sjfloat/mirage-vagrant-vms,yifanz/mirage-vagrant-vms,englishm/vagrant-xen,sjfloat/mirage-vagrant-vms,englishm/vagrant-xen,mirage/mirage-vagrant-vms,mirage/mirage-vagrant-vms,yifanz/mirage-vagrant-vms