Fix warning about forwardRef accepting exactly two params

This was the error:
```
Warning: forwardRef render functions accept exactly two parameters: props and ref. Did you forget to use the ref parameter?
```

src/RichTextEditor/RichTextEditor.tsx

@@ -115,7 +115,7 @@ const RichTextEditor = forwardRef((
     placeholder,
     customExtensions = [],
   }: RichTextEditorProps,
-  ref: ForwardedRef<RichTextEditorRef> = null,
+  ref: ForwardedRef<RichTextEditorRef>,
 ) => {
   const oneLineExtension = isOneLine ? [OneLineLimit] : [];