Handling dataset redirects
Currently datasets-server doesn't appear to handle dataset redirects, and gives an error. 

For example: 
- Querying `datasets` endpoints with the dataset `squad` works

- Querying `datasets-server` endpoints with the dataset `squad` gives an "unknown error"
- Querying `datasets-server` endpoints with a random dataset name (e.g. `xyz2309348`) gives an expected response (e.g. dataset unknown/doesn't exist)
- Querying `datasets-server` endpoints with the redirected name (`rajpurkar/squad`) works. 
Handling dataset redirects: Currently datasets-server doesn't appear to handle dataset redirects, and gives an error. 

For example: 
- Querying `datasets` endpoints with the dataset `squad` works

- Querying `datasets-server` endpoints with the dataset `squad` gives an "unknown error"
- Querying `datasets-server` endpoints with a random dataset name (e.g. `xyz2309348`) gives an expected response (e.g. dataset unknown/doesn't exist)
- Querying `datasets-server` endpoints with the redirected name (`rajpurkar/squad`) works. 