message: fix not_covered anchor
diff: @@ -60,7 +60,8 @@ patch versions. The public APIs consist of
  * [`tensor_shape`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/tensor_shape.proto)
  * [`types`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/types.proto)
  -## What is *not* covered {not_covered}
  +<a name="not_covered"></a>
  +## What is *not* covered
  Some API functions are explicitly marked as "experimental" and can change in
  backward incompatible ways between minor releases. These include:
  