Fixed bug in merging step_runner.py.
Fixed bug in merging step_runner.py.

StanfordBioinformatics/xppf,StanfordBioinformatics/loom,StanfordBioinformatics/xppf,StanfordBioinformatics/loom,StanfordBioinformatics/loom,StanfordBioinformatics/loom,StanfordBioinformatics/xppf,StanfordBioinformatics/xppf