setup.sh line 21 should be `source $current_directory/bin/activate`

Since `bin` is at the root of the project, and line 18 of `setup.sh` is a `cd` into `$current_directory/backend/`, the `activate` sourcing fails with a path error.

To fix, change `setup.sh` line 21
```
source bin/activate
```
to
```
source $current_directory/bin/activate
```
