Update sourcetree-beta to 2.6.2b1 (#4305)

Casks/sourcetree-beta.rb

@@ -1,11 +1,11 @@
 cask 'sourcetree-beta' do
-  version '2.6.1b1'
+  version '2.6.2b1'
-  sha256 '51c2cc556c637cb147f1d6b8b8c8a259a735bca8ad3ce75ff0024313f6bfe688'
+  sha256 'e5f650db0ed41afafde75180114ae30701d32241670b92bb7677a7d6f65b42d6'
 
   # atlassian.com was verified as official when first introduced to the cask
   url "https://downloads.atlassian.com/software/sourcetree/SourceTree_#{version}.zip"
   appcast 'https://www.sourcetreeapp.com/update/SparkleAppcastBeta.xml',
-          checkpoint: 'd21837fefdfa6f72f08454de4c5f3c54f4856b14dae9c9e49ed9b4285839f8c1'
+          checkpoint: 'bd6cc9a4f00221498884e11dbb17f033ce6f733b7008e42b0703a2fc3f51f832'
   name 'Atlassian SourceTree'
   homepage 'https://www.sourcetreeapp.com/'