Here’s a quick patch to switch from the deprecated get_all_category_ids function to the get_terms() function added in 4.0. I made the decision to use the 4.5 syntax but we could also use the 4.0 syntax if backwards compatibility was wanted see get_terms() for more.

Patch is here:
https://gist.github.com/BandonRandon/66075fcc3471ce104b77fc5fbb13feaf