Update How_to_count_tokens_with_tiktoken.ipynb (openai#511)

Add support for gpt-3.5-*-0613 models

Author: averykhoo

examples/How_to_count_tokens_with_tiktoken.ipynb

@@ -441,13 +441,16 @@
     "    if model == \"gpt-3.5-turbo\":\n",
     "        print(\"Warning: gpt-3.5-turbo may change over time. Returning num tokens assuming gpt-3.5-turbo-0301.\")\n",
     "        return num_tokens_from_messages(messages, model=\"gpt-3.5-turbo-0301\")\n",
+    "    elif model == \"gpt-3.5-turbo-16k\":\n",
+    "        print(\"Warning: gpt-3.5-turbo-16k may change over time. Returning num tokens assuming gpt-3.5-turbo-16k-0613.\")\n",
+    "        return num_tokens_from_messages(messages, model=\"gpt-3.5-turbo-16k-0613\")\n",
     "    elif model == \"gpt-4\":\n",
     "        print(\"Warning: gpt-4 may change over time. Returning num tokens assuming gpt-4-0314.\")\n",
     "        return num_tokens_from_messages(messages, model=\"gpt-4-0314\")\n",
     "    elif model == \"gpt-3.5-turbo-0301\":\n",
     "        tokens_per_message = 4  # every message follows <|start|>{role/name}\\n{content}<|end|>\\n\n",
     "        tokens_per_name = -1  # if there's a name, the role is omitted\n",
-    "    elif model == \"gpt-4-0314\":\n",
+    "    elif model in {\"gpt-4-0314\", \"gpt-3.5-turbo-0613\", \"gpt-3.5-turbo-16k-0613\"}:\n",
     "        tokens_per_message = 3\n",
     "        tokens_per_name = 1\n",
     "    else:\n",