Update image pattern in gulpfile to accommodate missing images

[dgiessing]

Closes #20553

[timvandermeij]

Looks good to me, with the comment addressed and the commits squashed into one (see https://github.com/mozilla/pdf.js/wiki/Squashing-Commits).

[timvandermeij]

Please fix the linting and squash the commits into one, with a good commit message (see https://github.com/mozilla/pdf.js/wiki/Squashing-Commits if you're not familiar with how to do that). It looks like after that this should be good to merge.

[dgiessing]

@timvandermeij Should be good to go now. It shows changes of another file because I merged the master into the patch?

[calixteman]

You can update your master branch and then rebase your branch.

[dgiessing]

You can update your master branch and then rebase your branch.

Thank you for bearing with me should be good to go now!

[timvandermeij]

Thank you for your contribution!