Update iterm2-beta to 3.1.beta.8 (#4322)

* Update iterm2-beta to 3.1.beta.8

* Update iterm2-beta.rb

Casks/iterm2-beta.rb

@@ -1,11 +1,11 @@
 cask 'iterm2-beta' do
   # note: "2" is not a version number, but an intrinsic part of the product name
-  version '3.1.beta.7'
+  version '3.1.beta.8'
-  sha256 '98f7cbfbe3ca7babae137338522a5535622ef33c06d2363c81850128822b48d5'
+  sha256 '336d1aa3aa8cde24e9efd8eb9adba0c2f894e965c93ae5d9a0217fdbeaae8b3f'
 
   url "https://iterm2.com/downloads/beta/iTerm2-#{version.dots_to_underscores}.zip"
   appcast 'https://iterm2.com/appcasts/testing3.xml',
-          checkpoint: '1f5f58e0134568646392e173eff1974cf0044c8b561a913e742516e84cc1c1fd'
+          checkpoint: '3e72538422bcf49dacaf62123e72b279306689b3ee29cc72d9ebce7e7d05af76'
   name 'iTerm2'
   homepage 'https://www.iterm2.com/'