Added a more portable way to determine shell
Added a more portable way to determine shell

Thanks to @gkappel
References #376

bshelton229/teleport,suedadam/teleport,gravitational/teleport,sokoow/teleport,aashley/teleport,suedadam/teleport,tidalf/teleport,sokoow/teleport,yacloud-io/teleport,yacloud-io/teleport,gravitational/teleport,sokoow/teleport,suedadam/teleport,bshelton229/teleport,yacloud-io/teleport,tidalf/teleport,bshelton229/teleport,bshelton229/teleport,aashley/teleport,ajvb/teleport,suedadam/teleport,gravitational/teleport,aashley/teleport,yacloud-io/teleport,sokoow/teleport,tidalf/teleport,sokoow/teleport,yacloud-io/teleport,sokoow/teleport,gravitational/teleport,ajvb/teleport,gravitational/teleport,bshelton229/teleport,ajvb/teleport,yacloud-io/teleport,tidalf/teleport,ajvb/teleport,aashley/teleport,gravitational/teleport,yacloud-io/teleport,ajvb/teleport,aashley/teleport,tidalf/teleport,suedadam/teleport