Fix compilation of algebra/auth in Coq 8.6

The rewrite auth_validN_eq was not performed in the hypothesis. It
used to work in 8.5 because of magic.

algebra/auth.v

@@ -155,7 +155,7 @@ Proof.
   - intros [[[?|]|] ?]; rewrite /= ?auth_valid_eq
       ?auth_validN_eq /= ?cmra_included_includedN ?cmra_valid_validN;
       naive_solver eauto using O.
-  - intros n [[[]|] ?] ?; rewrite auth_validN_eq;
+  - intros n [[[]|] ?]; rewrite !auth_validN_eq /=;
       naive_solver eauto using cmra_includedN_S, cmra_validN_S.
   - by split; simpl; rewrite assoc.
   - by split; simpl; rewrite comm.