ChEMBL version set to "latest "

You should be able to just download the latest version of ChEMBL without specifying a version

This is possible in `chembl_downloader` see below. 

```
Download the Latest Version
You can modify the previous code slightly by omitting the version keyword argument to automatically find the latest version of ChEMBL:

import chembl_downloader

path = chembl_downloader.download_extract_sqlite()
```