low effort typo fix (#184)

defualt => default
diff --git a/google/auth/compute_engine/_metadata.py b/google/auth/compute_engine/_metadata.py
index b35775a..9a22d7a 100644
--- a/google/auth/compute_engine/_metadata.py
+++ b/google/auth/compute_engine/_metadata.py
@@ -88,7 +88,7 @@
         request (google.auth.transport.Request): A callable used to make
             HTTP requests.
         path (str): The resource to retrieve. For example,
-            ``'instance/service-accounts/defualt'``.
+            ``'instance/service-accounts/default'``.
         root (str): The full path to the metadata server root.
         recursive (bool): Whether to do a recursive query of metadata. See
             https://cloud.google.com/compute/docs/metadata#aggcontents for more