Use tf.clip_by_value again in PR curves demo (#1150)
Use tf.clip_by_value again in PR curves demo (#1150)

Previously, #1132 had circumvented the use of `tf.clip_by_value` within the PR curves demo because it was buggy.

However, that behavior seems to have been fixed.
tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard