Use sort_by in missing deps doctor check

Library/Homebrew/cmd/doctor.rb

@@ -891,16 +891,16 @@ end
 
 def check_missing_deps
   return unless HOMEBREW_CELLAR.exist?
-  s = Set.new
+  missing = Set.new
   Homebrew.missing_deps(Formula.installed).each_value do |deps|
-    s.merge deps
+    missing.merge(deps)
   end
 
-  if s.length > 0 then <<-EOS.undent
+  if missing.any? then <<-EOS.undent
     Some installed formula are missing dependencies.
     You should `brew install` the missing dependencies:
 
-        brew install #{s.to_a.sort * " "}
+        brew install #{missing.sort_by(&:name) * " "}
 
     Run `brew missing` for more details.
     EOS