Fix error-code 2 on cargo run 🐞

[tgotwig]

relates clap-rs/clap#1264

With fish-shell:

↪ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.27s
     Running `target/debug/vid_merger`
vidmerger 0.1.2
Thomas Gotwig <tgotwig@gmail.com>
A wrapper around ffmpeg which simlifies merging multiple videos 🎞

USAGE:
    vid_merger <DIR> --format <format>

ARGS:
    <DIR>    Sets the input file to use

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -f, --format <format>    Sets a format

↪ echo $status
2

[tgotwig]

Hmmm after taking a look to other programs, this seems to be the default behavour when the help says that some arguments are required 🧐