[v4] Avoid hard-coding version in `pkg/version/version.go`

[AkihiroSuda]

rootlesskit/pkg/version/version.go

Line 3 in 62d2101

const Version = "3.1.0"

RootlessKit v4 will no longer hard-code the version in pkg/version/version.go.
The version will be resolved via the git tag on make.
The version cannot be detected correctly when the source is fetched as a non-git tar.gz archive.

Will affect packages, such as:

• https://github.com/Homebrew/homebrew-core/blob/main/Formula/r/rootlesskit.rb