"1.0.0-beta.2" should be less than "1.0.0-beta.11"

Hi.

Thank you for cpp-semver.

`semver::lt("1.0.0-beta.2", "1.0.0-beta.11")` should return `true`, but it returns `false`.

From https://semver.org:
```
1.0.0-beta.2 < 1.0.0-beta.11
```

Related to https://github.com/easz/cpp-semver/issues/7

Thank you.