Remove + on Skylark dicts (#863)
Remove + on Skylark dicts (#863)

The `+` operator on dicts is deprecated and will be removed from Bazel.
qiuminxu/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard