Apply suggestion: "tpu='local'".

Author: MarkDaoust

site/en/guide/tpu.ipynb

@@ -128,7 +128,7 @@
       },
       "outputs": [],
       "source": [
-        "resolver = tf.distribute.cluster_resolver.TPUClusterResolver()\n",
+        "resolver = tf.distribute.cluster_resolver.TPUClusterResolver(tpu='local')\n",
         "tf.config.experimental_connect_to_cluster(resolver)\n",
         "# This is the TPU initialization code that has to be at the beginning.\n",
         "tf.tpu.experimental.initialize_tpu_system(resolver)\n",