Bump dalli from 2.7.10 to 2.7.11
Bump dalli from 2.7.10 to 2.7.11

Update the gem to prevent the error:
```
Could not find cache store adapter for mem_cache_store (cannot load such 
file -- dalli)
/app/config/environment.rb:5:in `<top (required)>'
```

This is similar to the issues encountered in: 
https://github.com/alphagov/collections/commit/d8a6a51378e8bc37122a558e895ab7610916f179

alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall