[Bug]: The package product can't be used as a dependency

[Ryo Aoyama]

Checklist

• This is not a bug caused by platform.
• Reviewed the README and documentation.
• Checked existing issues & PRs to ensure not duplicated.

What happened?

When you try to use this package as a dependency, Xcode shows the following error.

The package product 'Atoms' cannot be used as a dependency of this target because it uses unsafe build flags.

Expected Behavior

The package is usable without any error.

Reproduction Steps

1. Add the package as a dependency of your project through Xcode.
2. Build it.

Swift Version

5.6

Library Version

0.1.0

Platform

iOS, tvOS, macOS, watchOS

Scrrenshot/Video/Gif

No response

[Ryo Aoyama]

Fixed by #6