Added gitlabr R client to applications.yml

Merged username-removed-40640 requested to merge jirkalewandowski/www-gitlab-com:master into master

This adds the R package gitlabr, which provides bindings to the Gitlab API, to the applications list. I do not provide screenshots, as it is a scripting interface. Example code can be found under https://github.com/jirkalewandowski/gitlabr#quick-start-example and a more extensive description in the R vignette.