settings: Change Update.download_dir to a PathBuf
settings: Change Update.download_dir to a PathBuf

The download_dir represents a Path so it is better mapped to a PathBuf
struct then a String.

Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

UpdateHub/updatehub