not linting jsx files

[Zauberfisch]

I've started a new module from silverstripe-module but I renamed all files that contain jsx syntax to ___.jsx.
Now I don't get any linting on those files anymore.
For example console.log() should produce a warning Unexpected console statement from the rule no-console, but it does not.

Filing this as a bug, because I see there are rules to allow .jsx extensions in webpack. So we should also lint those files.