Bump up version of tensorflow (#183) #369

Job	Run time
Test Code (data/utils)	1m 11s
Test Code (data/datasets/multicoil)	1m 16s
Test Code (data/datasets/*.py)	1m 34s
Test Code (models)	3m 37s
Test Code (training_scripts/denoising)	1m 8s
Test Code (training_scripts/multi_coil)	2m 41s
Test Code (training_scripts/dealiasing_train_test.py)	1m 39s
Test Code (training_scripts/ncpdnet_train_test.py)	4m 25s
Test Code (training_scripts/unet_nc_train_test.py)	1m 43s
Test Code (training_scripts/updnet_train_test.py)	3m 32s
Test Code (training_scripts/xpdnet_train_test.py)	3m 41s
	26m 27s

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