Add judging condition for function areAlreadyProcessed #35

Hello!
I use DExecutor for task scheduling, and I find that in some case, one node is skiped, but it's out coming node will still be executed. After debug for hours, I find that modifing the code here may be helpful.
I changed this place to "return this.processedNodes.stream().filter(Node::isSuccess).collect(Collectors.toSet()).containsAll(nodes);",and it worked.