fix missing conf.pri error

```
Checking for GeoIP Database (optional) ... yes
Checking for qtsingleapplication library ... [system]  yes
WARNING: /home/leigh/development/rpmbuild/BUILD/qBittorrent-release-3.1.0/unixconf.pri:2: Unable to find file for inclusion /home/leigh/development/rpmbuild/BUILD/qBittorrent-release-3.1.0/conf.pri
Project MESSAGE: Project is built in DEBUG mode.
WARNING: /home/leigh/development/rpmbuild/BUILD/qBittorrent-release-3.1.0/src/src.pro:82: Unable to find file for inclusion qtsingleapp/qtsingleapplication.pri
Project MESSAGE: GeoIP database will not be embedded in qBittorrent executable.
Project MESSAGE: Building translations
Project MESSAGE: Processing lang/qbittorrent_fr
```