Add build date via ldflags

[vassilevsky]

GoReleaser conveniently has the date field in RFC3339 format, which is very similar to ISO 🙃

https://goreleaser.com/customization/#Name%20Templates

[0crat]

@g4s8/z please, pay attention to this pull request

[0crat]

@vassilevsky/z this pull request is too small, just 9 lines changed (less than 10), there will be no formal code review, see §53 and §28; in the future, try to make sure your pull requests are not too small; @g4s8/z please review this and merge or reject

[g4s8]

@vassilevsky thanks, looks good, just few comments about PR style:

1. Please don't use Github keywords in PRs, such as closes #6 - 0crat will pay only if the ticket is closed by author or ARC, when you use closes keyword, the ticket will be closed by rultor merge bot and 0crat won't pay.
2. Add issue number to the commit message to be able to understand ticket number for any change later, it should look like: #6 - Add build date via ldflags

[vassilevsky]

I've fixed these issues 🤓

[g4s8]

@vassilevsky thanks

[g4s8]

@rultor merge

[rultor]

@rultor merge

@g4s8 OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge

@g4s8 Done! FYI, the full log is here (took me 2min)

[0crat]

Job gh:g4s8/gitstrap#17 is not assigned, can't get performer

[0crat]

This job is not in scope