message: Fix docs rendering in placeholder docs page.
diff: @@ -1718,7 +1718,9 @@ def placeholder(dtype, shape=None, name=None):
  print(sess.run(y, feed_dict={x: rand_array})) # Will succeed.
  ```
  - @compatibility{eager} Placeholders are not compatible with eager execution.
  + @compatibility(eager)
  + Placeholders are not compatible with eager execution.
  + @end_compatibility
  Args:
  dtype: The type of elements in the tensor to be fed.
  