interpret `--` as stdin about shelljs

[nfischer]

@neonstalwart Do you mean to modify shjs to allow the equivalent of this?

$ echo 'echo foo' | bash

If so, I think this will work as required:

$ echo "require('shelljs/global'); echo('foo');" | node

I'm closing this, since this seems to solve the issue. If this isn't sufficient, let me know, and we can reopen.

[neonstalwart]

I'm not sure if it's equivalent to what I meant but I've moved on quite a
lot since the time I opened this and no longer care.