fix: use currentSrc for imgs in <picture> tags

[fennifith]

Summary

Issue #174 details a lack of support for differences in the selected image within a <picture> tag. In this case, the image's currentSrc reflects which of the available sources the browser decided to use.

In my case, the <img> tags lack any src whatsoever, so when used outside of the <picture> tags they will not display any image.

Result

I took a slightly more naive solution than what is described in #174 - any <img> tag in a <picture> structure now sets zoomed.src = original.currentSrc after cloning the element. This ensures that the zoomed image will reflect the same source as what was originally displayed in the <picture> tag, and eliminates any flicker in the transition when used with data-zoom-src.

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[francoischalifour]

Closes #174.

[francoischalifour]

🎉 This was released in v1.0.8.

[fennifith]

Awesome - thank you! \:D