Handle 403 error properly for organizations

[orchestr7]

$ git-stat.bat -t stargazers -o artipie -e

[INFO] getting statistics for the following repositories: null
[ERROR] Please check the name of your repo. Not able to access https://api.github.com/repos/artipie/white-paper/stargazers?per_page=100&page=1 repository to get statistics <io.ktor.client.features.ClientRequestException: Client request(https://api.github.com/repos/artipie/white-paper/stargazers?per_page=100&page=1) invalid: 403 rate limit exceeded> (you can enable debug mode by --debug/-d option)