fix: URL to langchain agents page (#942)

Co-authored-by: Shyamal H Anadkat <shyamal@openai.com>

examples/How_to_build_a_tool-using_agent_with_Langchain.ipynb

@@ -185,7 +185,7 @@
    "source": [
     "## LLM Agent\n",
     "\n",
-    "An [LLM agent](https://python.langchain.com/en/latest/modules/agents/agents/custom_llm_agent.html) in Langchain has many configurable components, which are detailed in the Langchain documentation.\n",
+    "An [LLM agent](https://python.langchain.com/docs/modules/agents/) in Langchain has many configurable components, which are detailed in the Langchain documentation.\n",
     "\n",
     "We'll employ a few of the core concepts to make an agent that talks in the way we want, can use tools to answer questions, and uses the appropriate language model to power the conversation.\n",
     "- **Prompt Template:** The input template to control the LLM's behaviour and how it accepts inputs and produces outputs - this is the brain that drives your application ([docs](https://python.langchain.com/en/latest/modules/prompts/prompt_templates.html)).\n",