message: Update version info now that 1.15 is stable
diff: @@ -6,8 +6,7 @@ degradation in model accuracy. You can perform these techniques using an
  already-trained float TensorFlow model when you convert it to TensorFlow Lite
  format.
  -Note: The procedures on this page require TensorFlow 1.15 or higher (available
  -with the `tf-nightly` build).
  +Note: The procedures on this page require TensorFlow 1.15 or higher.
  ### Optimization options
  