Show devtools when launched with --dev argument

i haven't found a good way to send just a plain `--dev` switch via
powershell, so i send a `--dev=true`. If i send a plain `--dev` argument
i get a message saying that i don't have a proper atom app.

i'll might add a node module to handle this. This is just proof of
concept.
Bump atom-shell version

The newer atom-shell seems to be more forgiving with the arguments i
struggled with earlier.
Adjust the dev argument