Latest Version is broken on react native

[ivan-jorge001]

This break react native because it does have a window object defined but doesnt have that method, can we use
import { encode as btoa } from 'base-64';

nostr-react/src/core.tsx

Line 182 in aa23062

typeof window !== "undefined" ? window.btoa(JSON.stringify(filter)) : null

[ivan-jorge001]

PR to fix it #30