pip downloads 258 versions of boto3

As of commit d429483186d01eb1e6ffd449986632ee3eb57850,
```
$ grep -o 'Downloading [^-]*' pip.log | sort | uniq -c | sort -nr | head -4
258 Downloading boto3
9 Downloading django_admin_rangefilter
6 Downloading botocore
2 Downloading s3transfer
```
As the man says,
```
...
Downloading boto3-1.12.26-py2.py3-none-any.whl (128 kB)
Downloading boto3-1.12.25-py2.py3-none-any.whl (128 kB)
Downloading boto3-1.12.24-py2.py3-none-any.whl (128 kB)
INFO: This is taking longer than usual. You might need to provide the dependency resolver with stricter constraints to reduce runtime. If you want to abort this run, you can press Ctrl + C to do so. To improve how pip performs, tell us what happened here: https://pip.pypa.io/surveys/backtracking
```

Full log: [pip.log](https://github.com/code4romania/covid-19-ro-help/files/6370376/pip.log)

Not fatal, just an optimization.

Start by reproducing the dependency installation from commit d429483186d01eb1e6ffd449986632ee3eb57850 and compare it with the attached pip.log. Investigate why pip downloads 258 boto3 versions; done means the same installation completes with substantially less backtracking while preserving the required dependencies.

Written by the indexing model from the issue text.