Add the 'LineNo' to the cache key

### What is the problem / feature ?

If the user removes an item from the basket and re-adds it later on (same quantity) the `_build_cache_key` method will return the same key, and `data` will be loaded from the cache. Problem is that the `line.id` has changed and `RuntimeError` will be raised (`Unable to determine taxes on basket`).

### How did it get fixed / implemented ?

Add the `LineNo` to the caching key.

*Here is a cute animal picture for your troubles...*

![image](https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcTTJAYw95sf7jMpVRYccm33OxuU6-txAUWdlYEWtxzjVOgkUsmVDA)