Should be able to use a `number` as params to reverse a route

Hi, great lib btw :)

I ran into following problem:

```js
const RouteParser = require("route-parser")

const parser = new RouteParser("/courses/:id/trainings/:idx")

const route = parser.reverse({ id: "123", idx: "0" }) //  works just fine
// const route = parser.reverse({ id: "123", idx: 0 }) //  produces `false`

console.log(route)
```

Version     `"route-parser": "^0.0.5"`