update-report: add newline if preinstall updated.

Fixes #858.

Library/Homebrew/cmd/update-report.rb

@@ -76,7 +76,8 @@ module Homebrew
       if !ARGV.include?("--preinstall") && !ENV["HOMEBREW_UPDATE_FAILED"]
         puts "Already up-to-date."
       end
-    elsif hub.empty?
+    else
+      if hub.empty?
         puts "No changes to formulae."
       else
         hub.dump
@@ -84,6 +85,8 @@ module Homebrew
         hub.reporters.each(&:migrate_formula_rename)
         Descriptions.update_cache(hub)
       end
+      puts if ARGV.include?("--preinstall")
+    end
 
     link_manpages
     Tap.each(&:link_manpages)