Update address_similarity.curl

fix `postCode` casing in `/address-similarity` example

Author: seth-mg

examples/address_similarity.curl

@@ -8,7 +8,7 @@ curl -s -X POST \
             "road": "Pennsylvania Ave N.W.",
             "city": "Washington",
             "state": "DC",
-            "postcode": "20500"
+            "postCode": "20500"
           },
           "address2": "160 Pennsilvana Avenue, Washington, D.C., 20500"
         }' \