Update README.md

Author: Stephen Pinkerton

README.md

@@ -267,7 +267,7 @@ def lambda_handler(event, context):
   })
 ```
 
-## Datadog Tracer (**Experimental**)
+## Datadog Tracer (**Beta**)
 
 You can now trace Lambda functions using Datadog APM's tracing libraries ([dd-trace-py](https://github.com/DataDog/dd-trace-py)).