Thunderbird GL 31.6.0

Add tag stanza

Casks/thunderbird-gl.rb

@@ -1,10 +1,11 @@
 cask :v1 => 'thunderbird-gl' do
-  version '31.4.0'
+  version '31.6.0'
-  sha256 '36fe75ceae334fabbff74ed49a30755b87a9e2f1ec6af54551794151bd74021f'
+  sha256 'b0cc0e9bef5d62b82fcd37f57d03b852bcaadd9344d8ac1cb09bb6c1eca92a54'
 
   url "https://download.mozilla.org/?product=thunderbird-#{version}&os=osx&lang=gl"
   homepage 'https://www.mozilla.org/gl/thunderbird/'
   license :mpl
+  tags :vendor => 'Mozilla'
 
   app 'Thunderbird.app'
 end