(Disclaimer: I'm not an expert of OSS licenses.)
I'm happy to send a PR to fix this, but I feel a bit uneasy that there seems no credit to the original author of knitr in RStudio's source code. Are there any agreement between Yihui and RStudio to grant these lines of codes? Or, am I missing something?
Fortunately, knitr's license is GPL (GPLv2/GPLv3) and RStudio's license is AGPLv3, and GPLv3 and AGPLv3 can be considered compatible, so I believe there would be no actual problem. To be clear, I don't have a strong opinion on this and just want to avoid confusion.