Fix STD*_FILENO constants in JavaScript to match C

This updates settings.js so that the STD*_FILENO constants match unistd.h.

This does not change the values used for these handles as suggested by #1408, it merely changes the incorrect values in JavaScript to match the C constants. This solves my issue #1570.

I ran the existing standard tests and they pass:

```
Ran 2673 tests in 9656.070s

OK
```

I did not add/update any tests because I am unsure how to validate this in an automated fashion. Suggestions are welcome.