See the growth of the number of stars of a repository by accessing /#/{author}/{repository}.
e.g. If you want to see the growth of https://github.com/haya14busa/incsearch.vim, please access http://haya14busa.github.io/github-star-stats/#/haya14busa/incsearch.vim
I highly recommend you to authorize GitHub account because API access rate limit is too small without authorization.