scm: model: git: set revision graph support true (#5501)

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@7717 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/repository/git.rb

@@ -53,6 +53,10 @@ class Repository::Git < Repository
     true
   end
 
+  def supports_revision_graph?
+    true
+  end
+
   def repo_log_encoding
     'UTF-8'
   end