`tf.image.image_gradients`, `tf.image.sobel_edges`.
    *   Add links to https://js.tensorflow.org.
    *   Fix non-uniformity of orthogonal matrices.
    *   Fix bug where multi-image Estimator eval summaries were not displayed
        correctly.

<a name="rpc-issue"><sup>1</sup></a> The cancellation logic of the RPC op
contains a concurrency error. A fix has been submitted to master and will be
part of the next release.