message: Fix style issue in tfdbg documentation.
diff: @@ -346,7 +346,7 @@ line:
  diff = y_ * tf.log(y)
  ```
  -***tfdbg** has a feature that makes it easy to trace Tensors and ops back to
  +**tfdbg** has a feature that makes it easy to trace Tensors and ops back to
  lines in Python source files. It can annotate lines of a Python file with
  the ops or Tensors created by them. To use this feature,
  simply click the underlined line numbers in the stack trace output of the
  