Update libuweave/macaroon code

Added delegation time stamp into access token to match changed
validation logic of macaroons.

BUG: 26728665
Change-Id: I131b92b0e0b1b2274d80bdc0b5790a8c05071ec5
Reviewed-on: https://weave-review.googlesource.com/2467
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/third_party/libuweave/src/macaroon_caveat.h b/third_party/libuweave/src/macaroon_caveat.h
index 33f9d24..4905667 100644
--- a/third_party/libuweave/src/macaroon_caveat.h
+++ b/third_party/libuweave/src/macaroon_caveat.h
@@ -40,6 +40,9 @@
   kUwMacaroonCaveatScopeTypeViewer = 20,
 } UwMacaroonCaveatScopeType;
 
+// For security sanity checks
+#define UW_MACAROON_CAVEAT_SCOPE_LOWEST_POSSIBLE 127
+
 /** Compute the buffer sizes that are enough for caveat creation functions. */
 size_t uw_macaroon_caveat_creation_get_buffsize_(UwMacaroonCaveatType type,
                                                  size_t str_len);