Merge pull request #3524 from ksss/timestamp

MiniRake::Task#timestamp should use Time.now only

minirake

@@ -113,8 +113,7 @@ module MiniRake
     # Timestamp for this task.  Basic tasks return the current time for
     # their time stamp.  Other tasks can be more sophisticated.
     def timestamp
-      prerequisites = @prerequisites.collect{ |n| n.is_a?(Proc) ? n.call(name) : n }.flatten
-      prerequisites.collect { |n| Task[n].timestamp }.max || Time.now
+      Time.now
     end
 
     # Class Methods ----------------------------------------------------