message: Fix Missing r-string.
  The docs generator is not happy about the "\a" in "\approx" is becoming a "alert" escape sequence.
  This should also fix a lot of the mathjax rendering on this page:
diff: @@ -192,7 +192,7 @@ def _logspace_mean(log_values):
  def expectation(f, samples, log_prob=None, use_reparametrization=True,
  axis=0, keep_dims=False, name=None):
  - """Computes the Monte-Carlo approximation of \\(E_p[f(X)]\\).
  + r"""Computes the Monte-Carlo approximation of \\(E_p[f(X)]\\).
  This function computes the Monte-Carlo approximation of an expectation, i.e.,
  