Export Ascii for compat with new Coq

theories/proofmode/base.v

 From stdpp Require Export strings.
 From iris.algebra Require Export base.
-From Coq Require Import Ascii.
+From Coq Require Export Ascii.
 Set Default Proof Using "Type".
 
 (** * Utility definitions used by the proofmode *)

theories/proofmode/tokens.v

+Require Import Coq.Strings.Ascii.
 From iris.proofmode Require Import base.
 Set Default Proof Using "Type".