enable Array-type default export mock (#265)

[iambumblehead]

closes #265

thanks @altearius for the unit-test. It feels like you've finished this for me and adding three lines or so was effortless because of the test

[iambumblehead]

The main person who would normally review, @koshic, is usually not active during this time window, but it is probably safe to merge and publish nowish because the change is small and specific and probably safe

[koshic]

@iambumblehead thx for PR, looks safe )

[iambumblehead]

I learned these two things recently,

1. callbacks perform better than async-await
   • https://gist.github.com/weyoss/24f9ecbda175d943a48cb7ec38bde821?permalink_comment_id=4752197#gistcomment-4752197
2. regexp is slow; startsWith and endsWith are much faster, followed by equality operators ===
   • feat: optimise detection of data and svg names snabbdom/snabbdom#1057 (comment)