Add audit for unversioned URLs with checksum.

Library/Homebrew/cask/audit.rb

@@ -248,6 +248,7 @@ module Cask
       return unless cask.sha256
 
       check_sha256_no_check_if_latest
+      check_sha256_no_check_if_unversioned
       check_sha256_actually_256
       check_sha256_invalid
     end
@@ -260,6 +261,12 @@ module Cask
       add_error "you should use sha256 :no_check when version is :latest"
     end
 
+    def check_sha256_no_check_if_unversioned
+      return if cask.sha256 == :no_check
+
+      add_error "Use `sha256 :no_check` when URL is unversioned." if cask.url.unversioned?
+    end
+
     def check_sha256_actually_256
       odebug "Verifying sha256 string is a legal SHA-256 digest"
       return unless cask.sha256.is_a?(Checksum)