Fixes an issue where timeout/depth could only be single-digit numbers

```
zoffix@ZofMain:/tmp/g$ prereq-grapher -t 30
isa check for "timeout" failed: timeout must be an integer
 at (eval 196) line 88.
```

The regex that checks the arguments in the old version of the code, only allowed a single digit for `timeout`/`depth` arguments. This pull fixes the issue.