Use Rugged::SORT_NONE instead of Rugged::SORT_DATE

Meaning of SORT_DATE was changed in libgit2.
See https://github.com/libgit2/libgit2/commit/82d4c0e6b841ae0e466bd97ab1faec0920a6b7a2

SORT_NONE is the order produced by "git log".

lib/gitlab/git/repository.rb

@@ -320,7 +320,7 @@ module Gitlab
       def log_by_walk(sha, options)
         walk_options = {
           show: sha,
-          sort: Rugged::SORT_DATE,
+          sort: Rugged::SORT_NONE,
           limit: options[:limit],
           offset: options[:offset]
         }
@@ -382,7 +382,7 @@ module Gitlab
       # a detailed list of valid arguments.
       def commits_between(from, to)
         walker = Rugged::Walker.new(rugged)
-        walker.sorting(Rugged::SORT_DATE | Rugged::SORT_REVERSE)
+        walker.sorting(Rugged::SORT_NONE | Rugged::SORT_REVERSE)
 
         sha_from = sha_from_ref(from)
         sha_to = sha_from_ref(to)
@@ -460,7 +460,7 @@ module Gitlab
         if actual_options[:order] == :topo
           walker.sorting(Rugged::SORT_TOPO)
         else
-          walker.sorting(Rugged::SORT_DATE)
+          walker.sorting(Rugged::SORT_NONE)
         end
 
         commits = []