doctor: 'raring' => 'ready'

It was pointed out that 'raring' is a rare word can be confusing to
non-native speakers.

Closes Homebrew/homebrew#18659, see that for details.

Library/Homebrew/cmd/doctor.rb

@@ -1100,7 +1100,7 @@ module Homebrew extend self
       end
     end
 
-    puts "Your system is raring to brew." unless Homebrew.failed?
+    puts "Your system is ready to brew." unless Homebrew.failed?
   end
 
   def inject_dump_stats checks