User/homedir expansion doesn't work

```
swift run -c release FuzzilliCli ... --storagePath=~/fuzz_out --importCorpus=~/fuzz_corpus ...
```

this throws a directory not found error, but if i manually expand it to `/home/user/fuzz_out`, etc, it works properly.

Guessing there is a Swift equivalent of `os.path.expanduser()` that could be used