Update Ruby version to 2.3 in README.md
Update Ruby version to 2.3 in README.md

Follow up 09222d403ec542d0b5661cb59f4b64c7d02bd45e

gauravtiwari/webpacker,rossta/webpacker,gauravtiwari/webpacker,rails/webpacker,rails/webpacker,rossta/webpacker,rossta/webpacker,gauravtiwari/webpacker,rossta/webpacker