No support for BigInt

[mzedeler]

const { toJSON } = require('transit-immutable-js')
const { Map } = require('immutable')
toJSON(Map().set(1n, 'test')

This results in Uncaught TypeError: Cannot use 'in' operator to search for 'toMap' in 1

The same goes for toJSON(Map().set('test', 1n)).

I may be able to add BigInt support if you're open for PRs.'

[glenjamin]

Yep, I’ll take a PR - as long as it gracefully skips registering when BigInt is not available.

Alternatively you should be able to add a custom decoder in your application