Fall back to GRAPH.QUERY when `GRAPH.RO_QUERY` is not available.

Fix: #123

GRAPH.RO_QUERY is unavailable in older versions. So fallback to GRAPH.QUERY when the command is not found.

While there's a way to always use GRAPH.QUERY by setting read_only to False, methods that try to fetch the labels and other properties are hardcoded to True.

    def labels(self):
        return self.call_procedure("db.labels", read_only=True).result_set

    def relationshipTypes(self):
        return self.call_procedure("db.relationshipTypes", read_only=True).result_set

    def propertyKeys(self):
        return self.call_procedure("db.propertyKeys", read_only=True).result_set

While we can have a param read_only to the above methods, introducing the same would actually change many methods that is calling the above methods directly or indirectly to have read_only param and that's huge.

So checking for unknown command while executing the query makes it a simple fix.

RedisGraph / redisgraph-py

Fall back to GRAPH.QUERY when `GRAPH.RO_QUERY` is not available. #124