[src/parser.rs] Loosen parse validation so that just the executable path suffices

[SamuelMarks]

EDIT: Curiously ./target/debug/makers --version and ./target/debug/makers --help now works but ./target/debug/cargo-make --version and ./target/debug/cargo-make --help work as if neither --help nor --version were provided

[sagiegurari]

if cargo make used to work, now why this parser needs fixing?
also, any change here needs to come with a test

[sagiegurari]

closing as not needed