Symbols in maps causes formatter to break

[samdesota]

Hey, thanks for this extension.

I get this error:

Custom Formatter Failed: Uncaught TypeError: Cannot convert a Symbol value to a number

When attempting to expand a immutable Map with symbols as keys.

[mattzeunert]

Hey Samuel, thanks for reporting! I don't have much time to work on this right now, but feel free to open a PR here and I'll update the extension.

[samdesota]

Awesome, going to work on this next few days. I did an initial attempt but couldn't reproduce when running the library myself, so will have to debug further.