`true` isn't considered as a keyword

[Playground](https://typescripttolua.github.io/play.html#src=(%7B%20true%3A%20true%2C%20false%3A%20false%20%7D)%3B%0A)

Input:
```ts
({ true: true, false: false });
```

Current Result:
```lua
local ____ = ({true = true, ["false"] = false})
```

Expected Result:
```lua
local ____ = ({["true"] = true, ["false"] = false})
```