Don't include the shell in the spk for go stacks.

[zenhack]

No description provided.

[zarvox]

In hindsight, you can accomplish this (less conveniently, perhaps) by editing the sandstorm-pkgdef.capnp after calling spk init to directly launch /opt/app/app rather than /opt/app/.sandstorm/launcher.sh.

@zenhack Do you mind if I revert this and merge #184 so things can work out-of-the-box for Windows users? As noted above, you can still achieve the "avoid including bash in the package" outcome.