Deprecation should note how to fix

[mperham]

rack/lib/rack/response.rb

Lines 35 to 39 in d3c545e

	def header
	warn 'Rack::Response#header is deprecated and will be removed in Rack 3.1', uplevel: 1
	headers
	end

Please add "use headers instead" to the user message so the user knows how to fix the deprecation.

[ioquatix]

Are you able to submit a PR? Thanks!

[mperham]

@ioquatix See #2173

[ioquatix]

Thanks Mike! Although small, this is a great improvement. Feel free to submit more PRs :)