modify grad check in test_imgproc.py so it passes on GTX 980
modify grad check in test_imgproc.py so it passes on GTX 980

animesh-garg/cgt,bstadie/cgt,bstadie/cgt,rohanraja/cgt_distributed,dementrock/cgt,animesh-garg/cgt,rohanraja/cgt_distributed,RichardWarfield/cgt,bstadie/cgt,RichardWarfield/cgt,dementrock/cgt,RichardWarfield/cgt,dementrock/cgt,animesh-garg/cgt,rohanraja/cgt_distributed,rohanraja/cgt_distributed