Remove expireKey when no timeout is given

Hi, you have a small bug in locache.
Example:

```js
locache.set("test", "abc", 10) // timeout 10 sec
locache.set("test", "abc") // no timeout, should always be accessible
// wait 15 seconds
locache.get("test") //=> null
```
I think the right behaviour should be to remove any expire settings if I omit the timeout.

Thanks