Fix deprecation warning [(#1801)](GoogleCloudPlatform/python-docs-samples#1801)

logging.warn -> logging.warning to fix "DeprecationWarning: The 'warn' function is deprecated, use 'warning' instead"

Author: andrewsg

packages/google-cloud-logging/samples/snippets/handler.py

@@ -36,7 +36,7 @@ def use_logging_handler():
     text = 'Hello, world!'
 
     # Emits the data using the standard logging module
-    logging.warn(text)
+    logging.warning(text)
     # [END logging_handler_usage]
 
     print('Logged: {}'.format(text))