Fix a few lint errors
diff --git a/google/auth/app_engine.py b/google/auth/app_engine.py
index 846bcec..ec89dc0 100644
--- a/google/auth/app_engine.py
+++ b/google/auth/app_engine.py
@@ -65,6 +65,9 @@
     Raises:
         EnvironmentError: If the App Engine APIs are unavailable.
     """
+    # pylint: disable=missing-raises-doc
+    # Pylint rightfully thinks EnvironmentError is OSError, but doesn't
+    # realize it's a valid alias.
     if app_identity is None:
         raise EnvironmentError(
             'The App Engine APIs are not available.')
@@ -92,6 +95,9 @@
         Raises:
             EnvironmentError: If the App Engine APIs are unavailable.
         """
+        # pylint: disable=missing-raises-doc
+        # Pylint rightfully thinks EnvironmentError is OSError, but doesn't
+        # realize it's a valid alias.
         if app_identity is None:
             raise EnvironmentError(
                 'The App Engine APIs are not available.')