Fix inconsistency in credential_issuer_metadata_jwt_vc_json.json

Per the definition of the data structure that this example shows, the `logo` of the display properties of a Credential should have an `uri` field instead of `url` field.

examples/credential_issuer_metadata_jwt_vc_json.json

@@ -77,7 +77,7 @@
                     "name": "University Credential",
                     "locale": "en-US",
                     "logo": {
-                        "url": "https://university.example.edu/public/logo.png",
+                        "uri": "https://university.example.edu/public/logo.png",
                         "alt_text": "a square logo of a university"
                     },
                     "background_color": "#12107c",