aspell-dictionaries: use sha256 for resources

Closes Homebrew/homebrew#37962.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/cmd/aspell-dictionaries.rb

@@ -32,7 +32,7 @@ module Homebrew
         resource "#{r.name}" do
           url "#{r.url}"
           mirror "#{r.mirrors.first}"
-          sha1 "#{r.cached_download.sha1}"
+          sha256 "#{r.cached_download.sha256}"
         end
 
       EOS