And of relevance to the original article, in Reviewable you can customize your review completion condition with a snippet of code it will run on your behalf and

And of relevance to the original article, in Reviewable you can customize your review completion condition with a snippet of code it will run on your behalf and post the result as a GitHub commit status, so you can have basically any approval system you want. One of the examples is a simple LGTM-based system like in OP. (Disclaimer: I run reviewable.io.)