Panic when the `--file` file is not found

[marcospb19]

$ cargo run -- sweep --file

thread 'main' panicked at src/main.rs:237:18:
Failed to load timestamp file: failed to read stamp file /home/marcospb19/cargo-sweep/sweep.timestamp

Caused by:
    No such file or directory (os error 2)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace