There are two reasons for this:
* We will soon roll out first-class support for other JVM languages and Clojure will be hosted on a different machine. Without this language: line Leiningen will still land on Ruby workers.
* :language key will at some point in the future be mandatory.
Finally, you still can override `install:`, `script:` or anything else, so there is no reason to not have `language:` in your .travis.yml.
