wayland: request appropriate compositor version to support buffer scale

wayland: request appropriate compositor version to support buffer scale

With the introduction of the use of buffer scaling in ed4fcee4ct we
must request version 3 of the compositor as that is the version of the
surface interface that adds this new functionality. See the following
commit in weston:

commit a85118c1b85df6fbf8f896dca971a5b79a94da71
Author: Jason Ekstrand <jason@jlekstrand.net>
Date:   Thu Jun 27 20:17:02 2013 -0500

    Use wl_resource_create() for creating resources

    This commit sets the version numbers for all added/created objects.  The
    wl_compositor.create_surface implementation was altered to create a surface
    with the same version as the underlying wl_compositor.  Since no other
    "child interfaces" have version greater than 1, they were all hard-coded to
    version 1.

    Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
https://bugzilla.gnome.org/show_bug.cgi?id=703817