Should the regex for deepProperties be improved?

Hi,

I open this issue because `deepProperties` doesn't work with keys that have numbers in them.

```js
const schema = {
type: 'object',
deepProperties: {
'/audio.2.0/requireForced': {
const: true,
},
},
};
```

this produces the following error:
```
Error: schema is invalid: data/allOf/0/items must be object,boolean, data/allOf/0/items must be object,boolean, data/allOf/0/items must be object,boolean, data/allOf/0/items must be object,boolean, data/allOf/0/items must be object,boolean, data/allOf/0/items must be object,boolean, data/allOf/0/items must be object,boolean, data/allOf/0/items must be object,boolean
```

After my research, I've seen that this is due to this line in the `deepProperties` getSchema function.

https://github.com/ajv-validator/ajv-keywords/blob/a11389b4d1934d360fb2a24dd920ec597295c8fc/src/definitions/deepProperties.ts#L33

This raises multiples questions to me:

1. is it compliant with the JSON Schema standard to have numbers part of string fields? (I wasn't able to properly find a answer for that)
2. Is this project maintained? (I've seen that the last commit was 2 years ago.)
2.1 if yes -> Is a PR welcome to update that?
2.2 if no -> If it's not maintained anymore I can probably fork it and modify it for ourselves. And not bother you more (sorry for the Issue)