No Rakefile found when adding travis to a github project

I’m trying to add travis to my github project, and the build fails with:

$ rake
rake aborted!
No Rakefile found (looking for: rakefile, Rakefile, rakefile.rb, Rakefile.rb)
/home/travis/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in `eval'
/home/travis/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in `<main>'
(See full trace by running task with --trace)
The command "rake" exited with 1.

This is the most confusing error I’ve seen in several years, since I don’t have ruby in my project at all. I figured out that it’s basically “generic travis error” but that doesn’t help me figure out what’s wrong. There’s an answer on S/O that says to check the name of my file, but it is correct, it’s in the right branch, the formatting looks fine to me, and I have absolutely no leads on what to do next.
Here is my repository, this build is happening on the “develop” branch:

Any help making this work would be very helpful, or any explanation of why travis doesn’t run checks to throw descriptive errors for things like whatever this is would at least make this less frustrating even if I have to find another CI tool.

Ah, it means “no language specified”, I figured it out.