fix: Change max_tokens to trigger in middleware config (#1234)

## Overview

Fixed a typo in Context Edit Middleware docs. 

## Type of change

**Type:** typofix

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## Additional notes
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Author: pyaf

src/oss/langchain/middleware.mdx

@@ -1077,7 +1077,7 @@ agent = create_agent(
     middleware=[
         ContextEditingMiddleware(
             edits=[
-                ClearToolUsesEdit(max_tokens=1000),  # Clear old tool uses
+                ClearToolUsesEdit(trigger=1000),  # Clear old tool uses
             ],
         ),
     ],