fix find warnings and use tr instead of basename

Attempt to mitigate the following CI warnings:

```
find: warning: you have specified the -maxdepth option after a non-option argument -type, but options are not positional (-maxdepth affects tests specified before it as well as those specified after it).  Please specify options before other arguments.
find: warning: you have specified the -mindepth option after a non-option argument -type, but options are not positional (-mindepth affects tests specified before it as well as those specified after it).  Please specify options before other arguments.
basename: extra operand `./point-mutations'
```

They don't seem to cause a build failure; however, they are annoying.