Update make_simple_step_size_update_policy

tfp.mcmc.make_simple_step_size_update_policy() requires num_adaptation_steps as an argument. I am not sure if the correct value is None but it gives the same results as the PyMC3 version of this notebook.

Author: hsm207

Diff for: Chapter1_Introduction/Ch1_Introduction_TFP.ipynb

@@ -1273,7 +1273,7 @@
         "            target_log_prob_fn=unnormalized_log_posterior,\n",
         "            num_leapfrog_steps=2,\n",
         "            step_size=step_size,\n",
-        "            step_size_update_fn=tfp.mcmc.make_simple_step_size_update_policy(),\n",
+        "            step_size_update_fn=tfp.mcmc.make_simple_step_size_update_policy(num_adaptation_steps=None),\n",
         "            state_gradients_are_stopped=True),\n",
         "        bijector=unconstraining_bijectors))\n",
         "\n",