message: Fix small typo in RELEASE.md
diff: * The [distributions.Bijector](https://www.tensorflow.org/versions/r1.9/api_docs/python/tf/contrib/distributions/bijectors/Bijector)
  API supports broadcasting for Bijectors with new API changes.
  -## Breaking Chances
  +## Breaking Changes
  * If you're opening empty variable scopes; replace `variable_scope('', ...)` by
  `variable_scope(tf.get_variable_scope(), ...)`.
  