resouce file in tar break some automated build

I was investigating an issue with macbrew while I found the file `._pngquant_opts.c` that caused a warning in tar.
```
-rw-r--r--  0 501    20        176 22 Nov 00:59 pngquant-2.17.0/._pngquant_opts.c
tar: Ignoring malformed pax extended attribute
-rw-r--r--  0 501    20       5812 22 Nov 00:59 pngquant-2.17.0/pngquant_opts.c
```
There are workarounds, but it's better to get rid of it.