Fix cron.daily file name so it runs.

To quote the run-parts manpage.

```
       run-parts  runs  all  the  executable  files  named  within constraints
       described below, found in directory directory.  Other files and  direc‐
       tories are silently ignored.

       If neither the --lsbsysinit option nor the --regex option is given then
       the names must consist entirely of ASCII upper- and lower-case letters,
       ASCII digits, ASCII underscores, and ASCII minus-hyphens.
```