Appveyor CI IRC shows the wrong branch for pull requests

For example, the branch that Neel opened a pull request for is b23588, based on master:

11:49 appveyor-ci: torproject/tor master 1752b17 - Neel Chauhan: Add changes file for Bug #23588
11:49 appveyor-ci: Build #1.0.450 failed. Details: https://ci.appveyor.com/project/torproject/tor/build/1.0.450

If I can't fix this in a few minutes tomorrow, I'll leave it for later.