Return representation of `node` as keyword arg.

def visit_keyword(self, node: AST, dfltChaining: bool = True) -> str:
        """Return representation of `node` as keyword arg."""
        arg = node.arg
        if arg is None:
            return f"**{self.visit(node.value)}"
        else:
            return f"{arg}={self.visit(node.value)}"