Ruby has been continually decreasing on Github for a little while now. It makes more sense when you realize that Github was dominated by Ruby when it started out and other languages are still coming on to the platform in proportion. Try switching the view between percentage and total number and it becomes more clear.
on HN trends up to 2012 it was about the same as python or sometimes higher now Ruby is way below. The general trendline of up is the result of HN's Who is hiring thread popularity and increasing number of job posts in absolute numbers. Here it's more evident, Ruby was the most popular language 3 years ago
http://www.ryan-williams.net/hacker-news-hiring-trends/2015/...
