Cannot build within Docker

otherwise, you'll see this:
```
cp: cannot stat 'external/org_psutil/psutil/_psutil_linux.so': No such file or directory
Target //guild:guild failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 659.485s, Critical Path: 239.24s
FAILED: Build did NOT complete successfully
```