docs: fix a typo in UPGRADING.md related to static_discovery (#1956)

* docs: fix a typo in UPGRADING.md related to static_discovery

* fix wording

Author: parthea

UPGRADING.md

@@ -29,7 +29,7 @@ are included in the library. Users of private APIs should set the
 `static_discovery` argument of `discovery.build()` to `False` to continue to
 retrieve the service definition from the internet. As of version 2.1.0,
 for backwards compatibility with version 1.x, if `static_discovery` is not
-specified, the default value for `static_discovery` will be `True` when
+specified, the default value for `static_discovery` will be `False` when
 the `discoveryServiceUrl` argument of `discovery.build()` is provided.
 
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