How to set Pull Request build to trigger upon pushing to master?

John pushes to master, Circle builds master, status of master is green.
Jane branches off master, creates branch feature, changes some files and pushes. Circle builds the PR, and shows feature and master merge will be green.
John pushes to master, breaks the build/creates test conflict that will fail a feature merge. But…
Jane looks at her PR build. Which… is still green. So she merges and suddenly, master fails.

How can I make it so that every push to master will trigger the build for every PR?

Thanks.

+1. This is an issue for us. Travis will build both the Push and the PR, so if the base branch gets updated, the PR rebuilds. Since Circle doesn’t seem to have this option, we have to enable the option in GitHub to only allow merges from up-to-date branches. This requires a lot of unnecessary button mashing and merge commits when trying to close out a few non-conflicting PRs. Please add this feature!