Update airmail-beta to 3.3.3.450,315 (#4389)

Casks/airmail-beta.rb

@@ -1,11 +1,11 @@
 cask 'airmail-beta' do
-  version '3.3.3.449,314'
-  sha256 'ef20c55934ec700bb83bde293fdf66f2867e63f0bb064b3ceac5c31dabcc3f96'
+  version '3.3.3.450,315'
+  sha256 '29a3fe9afb3e050553de226b38735b8dbb74090d1dab1d003530e16863f46c0a'
 
   # 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: '1883a17711c0e7d25f0ddcb37085495d9b2bd8290a2d63631f0a0cb955e4b4f0'
+          checkpoint: 'ad9d1ce5a838fff3caca8c0d68cf7d6acd2a3e599c409d1c17f0d5016a051eb2'
   name 'Airmail'
   homepage 'http://airmailapp.com/beta/'