Silence git messages to stdout during app boot.

Caused this to be printed every time tests were run:

    git is /usr/bin/git
    /home/user/src/danbooru

config/application.rb

@@ -24,7 +24,7 @@ module Danbooru
 
     if File.exists?("#{config.root}/REVISION")
       config.x.git_hash = File.read("#{config.root}/REVISION").strip
-    elsif system("type git && git rev-parse --show-toplevel")
+    elsif system("type git > /dev/null && git rev-parse --show-toplevel > /dev/null")
       config.x.git_hash = %x(git rev-parse --short HEAD).strip
     else
       config.x.git_hash = nil