History file should include props for non-collaborators

[benbalter]

When you call @jekyllbot merge, and the bot updates the History file, if the author of the pull request isn't a collaborator/maintainer, the History file should give the author credit (e.g., props @benbalter), especially now that the history gets pulled into the release directly... the idea being that we should be giving credit where credit is due to encourage contributors.

[pathawks]

I wonder if this requires upstream changes to changelog, or if it would be better just appending to Summary?