Support pagination in compare

As per [this announcement](https://github.blog/changelog/2021-03-22-compare-rest-api-now-supports-pagination/), the Compare REST API now supports pagination of commits.

lib/octokit/client/commits.rb

@@ -189,13 +189,18 @@ def create_commit(repo, message, tree, parents=nil, options = {})
 
       # Compare two commits
       #
+      # When using auto_pagination, commits from all pages will be concatenated
+      # into the <tt>commits</tt> attribute of the first page's response.
+      #
       # @param repo [Integer, String, Hash, Repository] A GitHub repository
       # @param start [String] The sha of the starting commit
       # @param endd [String] The sha of the ending commit
       # @return [Sawyer::Resource] A hash representing the comparison
       # @see https://developer.github.com/v3/repos/commits/#compare-two-commits
       def compare(repo, start, endd, options = {})
-        get "#{Repository.path repo}/compare/#{start}...#{endd}", options
+        paginate "#{Repository.path repo}/compare/#{start}...#{endd}", options do |data, last_response|
+          data.commits.concat last_response.data.commits
+        end
       end
 
       # Merge a branch or sha