fix: Change the docs of JSONAgentOutputParser (#11594)

I am merely making some minor adjustments to the function documentation.
I hope to provide a small assistance to LangChain.
- **Description:** Change the docs of JSONAgentOutputParser. It will be
`JSON` better,
  - **Issue:** no,
  - **Dependencies:** no,
  - **Tag maintainer:** @hwchase17,
  - **Twitter handle:** Not worth mentioning.

libs/langchain/langchain/agents/output_parsers/json.py

@@ -11,7 +11,7 @@ logger = logging.getLogger(__name__)
 
 
 class JSONAgentOutputParser(AgentOutputParser):
-    """Parses tool invocations and final answers in XML format.
+    """Parses tool invocations and final answers in JSON format.
 
     Expects output to be in one of two formats.