Sort the commits on network graph by commiter date.

Author date is not updated, if the commits is rebased.
So the network graph having many rebased commit turns round and round,
that it is very difficult to undarstand history.

lib/gitlab/graph/json_builder.rb

@@ -33,7 +33,7 @@ module Gitlab
       #
       def collect_commits
 
-        @commits = Grit::Commit.find_all(repo, nil, {max_count: self.class.max_count, skip: to_commit}).dup
+        @commits = Grit::Commit.find_all(repo, nil, {topo_order: true, max_count: self.class.max_count, skip: to_commit}).dup
 
         # Decorate with app/models/commit.rb
         @commits.map! { |commit| ::Commit.new(commit) }
@@ -86,7 +86,7 @@ module Gitlab
 
       # Skip count that the target commit is displayed in center.
       def to_commit
-        commits = Grit::Commit.find_all(repo, nil)
+        commits = Grit::Commit.find_all(repo, nil, {topo_order: true})
         commit_index = commits.index do |c|
           c.id == @commit.id
         end