Update to Ruby and Rails supported versions (#2592)
Update to Ruby and Rails supported versions (#2592)

Addresses issue reported in #2590

Update the supported versions of both ruby and rails on the README.md
DigitalCurationCentre/roadmap,CDLUC3/dmptool,DigitalCurationCentre/roadmap,CDLUC3/dmptool,DMPRoadmap/roadmap,DMPRoadmap/roadmap,CDLUC3/dmptool,DigitalCurationCentre/roadmap,DMPRoadmap/roadmap,CDLUC3/dmptool