Warnings printed during the usage of html2md

[vogella]

Thank you for your great package.

If I use it, I see the following warnings:

../../.pub-cache/hosted/pub.dev/html2md-1.3.1/lib/src/converter.dart:108:41: Warning: Operand of null-aware operation '!' has type 'Node' which excludes null.
 - 'Node' is from 'package:html/dom.dart' ('../../.pub-cache/hosted/pub.dev/html-0.15.4/lib/dom.dart').
    sibling = util.previousSibling(node.node!);
                                        ^
../../.pub-cache/hosted/pub.dev/html2md-1.3.1/lib/src/converter.dart:111:37: Warning: Operand of null-aware operation '!' has type 'Node' which excludes null.
 - 'Node' is from 'package:html/dom.dart' ('../../.pub-cache/hosted/pub.dev/html-0.15.4/lib/dom.dart').
    sibling = util.nextSibling(node.node!);

Converter still works but maybe you want to silence these warnings.

[tomyeh]

It shall be the same as #41

@jarontai Any plan to release 1.3.2?

[jarontai]

Version 1.3.2 published, thank you!