No error messages showed in install.sh

Hello,

I don't know why but it's seems that stderr is also redirect to `/dev/null` in your install.sh file after a test on Debian Stretch and Archlinux.

If I add a `2` before `>`, like the following code, the stderr is showed and I know scanelf is not installed.
```
which scanelf 2> /dev/null
```

If it's normal that error messages isn't showed, I think it's a little strange...