I don't doubt there's bias against women, nor I want to mansplain the results at all. However I care deeply about good science and reliable facts. This article is not very good at showing clearly that this bias exists. Here are a few major problems with it:
1. Are the samples of women and men who post on GitHub representative of all open source programmers? I would think that women tend to contribute publicly less than man, and tend to disclose their gender less than men, and this probably biases the sample. The article doesn't attempt to analyze this, it merely assumes their sample is adequate.
2. The article says that both men and women get less pull requests accepted when their gender is identifiable, although this affects more women than men. The article does not compare the two values explicitly (in fact, it does not give the value for men at all), and it doesn't attempt to explain this effect -- it could well be that there's a confounding factor they haven't considered other then gender bias
3. Both men and women can accept and deny pull requests. Surely the gender of who accepts or denies the pull request is a factor that needs to be analyzed before the conclusion can be "there is gender discrimination"?