Merge common JSON and JSONB

conn.go

@@ -799,9 +799,7 @@ func (c *Conn) sendPreparedQuery(ps *PreparedStatement, arguments ...interface{}
 				err = encodeTimestampArray(wbuf, arguments[i], TimestampTzOid)
 			case OidOid:
 				err = encodeOid(wbuf, arguments[i])
-			case JsonOid:
-				err = encodeJson(wbuf, arguments[i])
-			case JsonbOid:
+			case JsonOid, JsonbOid:
 				err = encodeJson(wbuf, arguments[i])
 			default:
 				return SerializationError(fmt.Sprintf("Cannot encode %T into oid %v - %T must implement Encoder or be converted to a string", arg, oid, arg))