gojay generated code doesn't work for type names starting with K

When generating code with gojay, it does not support types starting with K. For example:

```go
type Key struct {...}
```

generates the code:

```go
func (k *Key) UnmarshalJSONObject(dec *gojay.Decoder, k string) error {
...
}
```

This doesn't compile, since both the alias and a argument use the same variable, k. 