Updated to tensorflow 1.15.0.

[tuh8888]

I updated the TensorFlow version from 1.2.0 to 1.15.0. The tests initially failed. I fixed them simply substituting the to-array fn for into-array fn in the outer array conversion in the tf-vals util fn. The problem was to-array returns an Object array while into-array uses the first value to box the array.

Now all tests pass and users can use the latest version of Java TensorFlow.