fix presentation request (#548)

Co-authored-by: Rodolfo Miranda <[email protected]>

src/keri/vc/protocoling.py

@@ -328,7 +328,7 @@ def do(self, tymth, tock=0.0, **opts):
                     data["schema"] = dict(
                         n=payload["s"]
                     )
-                if "i" in payload:
+                if "n" in payload:
                     data["credential"] = dict(
                         n=payload["n"]
                     )