upgrade thunderbird-cn to 31.2.0

Casks/thunderbird-cn.rb

@@ -1,8 +1,8 @@
 cask :v1 => 'thunderbird-cn' do
-  version '31.1.2'
-  sha256 '0a6520b64c16788e7aff8801d9b5c8e24b4a7c3f7967232a7e97b73bc803a177'
+  version '31.2.0'
+  sha256 'be5d5b95e6f747bba18cdaf5f746b16c44f563ca3e4bb735a9400c15a075b2b1'
 
-  url "http://ftp.mozilla.org/pub/mozilla.org/thunderbird/releases/#{version}/mac/zh-CN/Thunderbird%20#{version}.dmg"
+  url "ftp://ftp.mozilla.org/pub/mozilla.org/thunderbird/releases/#{version}/mac/zh-CN/Thunderbird%20#{version}.dmg"
   homepage 'https://www.mozilla.org/zh-CN/thunderbird/'
   license :oss