Bump Ruby version for Netlify

The site can build without Ruby; however, Netlify wants a Ruby version.
Pick something recent.

Author: Tim Bannister

netlify.toml

@@ -7,9 +7,9 @@ functions = "functions"
 command = "git submodule update --init --recursive --depth 1 && make non-production-build"
 
 [build.environment]
-HUGO_VERSION = "0.82.0"
 NODE_VERSION = "10.20.0"
-RUBY_VERSION = "2.7.1"
+HUGO_VERSION = "0.82.0"
+RUBY_VERSION = "3.0.1"
 
 [context.production.environment]
 HUGO_BASEURL = "https://kubernetes.io/"