Make `kill` return Unit instead of Boolean
Make `kill` return Unit instead of Boolean

The underlying implementation in `node/lib/internal/child_process.js` does
return a boolean value, but this value is devoid of any semantic content.

Shortened it does:

```
if childProcessHandle {
  res = child.kill(signal)
  if (res === 0) {
    child.killed = true;
    return true;
  else {
    throwError()
  }
}
else {
  return false;
}
```

which means the returned boolean depends on whether the subprocess still exists
and whether the signal was successfully sent (apparently the original author
thought that sending a signal will always kill the process).

The return value isn’t even mentioned in the documentation, so it must be a
historical artifact kept around for backward compatibility.

purescript-node/purescript-node-child-process