Update How_to_handle_rate_limits.ipynb (#554)

Replace deprecated model "code-cushman-001" with "gpt-3.5-turbo".

examples/How_to_handle_rate_limits.ipynb

@@ -132,9 +132,9 @@
     "\n",
     "# request a bunch of completions in a loop\n",
     "for _ in range(100):\n",
-    "    openai.Completion.create(\n",
-    "        model=\"code-cushman-001\",\n",
-    "        prompt=\"def magic_function():\\n\\t\",\n",
+    "    openai.ChatCompletion.create(\n",
+    "        model=\"gpt-3.5-turbo\",\n",
+    "        messages=[{\"role\": \"user\", \"content\": \"Hello\"}],\n",
     "        max_tokens=10,\n",
     "    )\n"
    ]