funcsave should update path to function

```fish
~> alias foo="bar"
~> type -p foo
-
~> funcsave foo
~> type -p foo
-
~> exec fish
~> type -p foo
/home/mqudsi/.config/fish/functions/foo.fish
```

This prevents the use of `funced` to edit the saved function, as the function loaded in memory is the one that is sourced when `funced foo` is used.