Try using language: c

Possibly a simpler environment. In any case, `language: racket` was a
"no-op documentation" resulting in some default, since Racket not
officially supported. I _think_ the default was Ruby, so trying C as a
maybe simpler/cleaner base.

.travis.yml

@@ -1,4 +1,4 @@
-language: racket
+language: c
 
 env:
  - RACKET_VERSION=5.3.5