Privacy Considerations: wording improvement.

Co-authored-by: Dave Longley <[email protected]>

index.html

@@ -1696,7 +1696,7 @@ <h4>Linkage via VC Processing</h4>
           <h4>Linkage via Proof Options and Mandatory Reveal</h4>
           <p>
 In the [[vc-data-integrity]] specification, a number of properties of the
-`proof` attribute of a VC are given. Care must be taken that optional fields
+`proof` attribute of a VC are given. Care has to be taken that optional fields
 ought not provide strong linkage across verifiers. The optional fields include:
 <em>id</em>, <em>created</em>, <em>expires</em>, <em>domain</em>,
 <em>challenge</em>, and <em>nonce</em>. For example the optional