Couldn't open SUMMARY.md in "./src" directory

[SWW13]

I'm no longer able to build my documentation with Fundoc 0.5.0. When the book/ dir and the book.toml file are present it still seems to work, but I don't have these laying around in a clean CI environment.

Minimal Reproducer:

mkdir -p /tmp/example
cd /tmp/example
mkdir -p crate/src
touch crate/src/main.rs
$EDITOR fundoc.json

fundoc.json:

{
  "docs_folder": "docs",
  "project_path": ".",
  "files_patterns": [
    "crate/**/*.rs"
  ],
  "mdbook": true,
  "book_build_dir": "book"
}

$ fundoc --version
Fundoc 0.4.1
$ fundoc
Start documentation parsing...


Documentation coverage: 0%
Done!
Summary is created

$ fundoc --version
Fundoc 0.5.0
$ fundoc
Start documentation parsing...


Documentation coverage: 0%
Done!
Summary is created
thread 'main' panicked at 'Unable to load the book: Couldn't open SUMMARY.md in "./src" directory

Caused by:
    No such file or directory (os error 2)', /home/simon/.cargo/registry/src/github.com-1ecc6299db9ec823/fundoc-0.5.0/src/book.rs:20:33
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace