chore: fix comment about clock_skew (#653)

Clock skew was changed in #581

Author: busunkim96

packages/google-auth/google/auth/credentials.py

@@ -63,7 +63,7 @@ def expired(self):
         if not self.expiry:
             return False
 
-        # Remove 5 minutes from expiry to err on the side of reporting
+        # Remove 10 seconds from expiry to err on the side of reporting
         # expiration early so that we avoid the 401-refresh-retry loop.
         skewed_expiry = self.expiry - _helpers.CLOCK_SKEW
         return _helpers.utcnow() >= skewed_expiry