updated airmail-beta (2.6.1)

Casks/airmail-beta.rb

@@ -1,9 +1,11 @@
 cask 'airmail-beta' do
-  version :latest
-  sha256 :no_check
+  version '2.6.1'
+  sha256 'df3f2c42a7ff30ac48cb012359fc4592e68adbd4d2de750b3e6145f3a65448de'
 
-  # hockeyapp.net is the official download host per the vendor homepage
+  # 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?format=zip'
+  appcast 'https://rink.hockeyapp.net/api/2/apps/84be85c3331ee1d222fd7f0b59e41b04',
+          checkpoint: '81963e6554a06178942678221adbd94f9dbe9c42a8fabfb01dbc951c06f7e9ff'
   name 'AirMail'
   homepage 'http://airmailapp.com/beta/'
   license :unknown # TODO: change license and remove this comment; ':unknown' is a machine-generated placeholder