Return `node`s value formatted according to its format spec.

def visit_FormattedValue(self, node: AST,
                             dfltChaining: bool = True) -> str:
        """Return `node`s value formatted according to its format spec."""
        format_spec = node.format_spec
        return f"{{{self.visit(node.value)}" \
               f"{self.CONV_MAP.get(node.conversion, '')}" \
               f"{':'+self._nested_str(format_spec) if format_spec else ''}}}"