Support `data-srcset`

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used patch-package to patch [email protected] for the project I'm working on.

I don't think it's a perfect solution but it might help someone else.

Here is the diff that solved my problem:

diff --git a/node_modules/html2amp/lib/utils.js b/node_modules/html2amp/lib/utils.js
index e17e685..a67a513 100644
--- a/node_modules/html2amp/lib/utils.js
+++ b/node_modules/html2amp/lib/utils.js
@@ -51,7 +51,7 @@ const normalizeSrc = (src, srcset) => {
 const remoteImgCaches = new Map()
 const srcNode = async (cwd, attributes) => {
   const { src, alt = '', ...attrs } = attributes
-  const url = normalizeUrl(normalizeSrc(src, attributes.srcset))
+  const url = normalizeUrl(normalizeSrc(src, attributes.srcset || attributes['data-srcset']))
   let size = { width: null, height: null }
   let result = null
   if (url.startsWith('http')) {

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