update_list cannot update element if the name is "x"

I know everything is ok if the element name is not `"x"`, which is the same name of the formal argument...

``` r
update_list(list(x = 1), x = 2)
#> Error: is.list(x) is not TRUE
```

Is it possible to use a list or named character vector instead?

``` r
update_list(list(x = 1), list(x = 2))
update_list(list(x = 1), c(x = 2))
```
