Update airmail-beta to 3.5.3.464,325 (#4892)

Casks/airmail-beta.rb

@@ -1,11 +1,11 @@
 cask 'airmail-beta' do
-  version '3.5.3.463,324'
-  sha256 '4982b6b4f79cad21a33b4cc467b56511975f30a3ffb546242f549c3db506f9ff'
+  version '3.5.3.464,325'
+  sha256 'c4454687d2d0945c7b6f9c55af3092b6325ce5f392e83d88e522dbd75b3b62ee'
 
   # hockeyapp.net/api/2/apps/84be85c3331ee1d222fd7f0b59e41b04 was verified as official when first introduced to the cask
   url "https://rink.hockeyapp.net/api/2/apps/84be85c3331ee1d222fd7f0b59e41b04/app_versions/#{version.after_comma}?format=zip&"
   appcast 'https://rink.hockeyapp.net/api/2/apps/84be85c3331ee1d222fd7f0b59e41b04',
-          checkpoint: '3ba7b864711bc4d2fc5c4c939b23edc191141a0a9c3b26bee4f3689452b58b6e'
+          checkpoint: '29185cf75de05f6f477a340ee54b45810bbda4f1ab238779ac9dbf61a7f0bfff'
   name 'Airmail'
   homepage 'http://airmailapp.com/beta/'