NW.js has to deal with javascript and certain browser functions; some versions of RPGMaker games use it. What that error is saying is that something on your computer used a higher/updated version of NW.js to perform a task. While Roundscape was using a older version. It's a harmless pop-up in a sense. However if you're like me, the pop can get annoying.
So to fix that here's what you do, at least for Windows 10:
-Open a file explorer and type in/get to "C:\Users\[Your Username]\AppData\Local". Or use windows key and R, get the run command box, and type "%localappdata%". Either works.
-Find the "nwjs" folder and delete it.
-In the same local app data folder find the folder "User Data". Open it.
-Find the folder "Default". Open it.
-Find the files "Web Data" and "Web Data-journal". Delete them.
-Exit out of the folders.
After all that's done open Roundscape and the pop-up should be gone.
Let me know if you need any extra help.
Check out the moderator Redknight's post
here.