[clojure mode] Modernize the style of the example code.
[clojure mode] Modernize the style of the example code.

[The Clojure Style Guide](https://github.com/bbatsov/clojure-style-guide).

codio/CodeMirror,wingify/CodeMirror,pabloferz/CodeMirror,namin/CodeMirror,mtaran-google/CodeMirror,dperetti/CodeMirror,wingify/CodeMirror,jkaplon/CodeMirror,namin/CodeMirror,codio/CodeMirror,thomasjm/CodeMirror,jkaplon/CodeMirror,hackmdio/CodeMirror,notepadqq/CodeMirror,namin/CodeMirror,dperetti/CodeMirror,SidPresse/CodeMirror,jkaplon/CodeMirror,notepadqq/CodeMirror,nightwing/CodeMirror,pabloferz/CodeMirror,nightwing/CodeMirror,notepadqq/CodeMirror,codio/CodeMirror,hackmdio/CodeMirror,dperetti/CodeMirror,pabloferz/CodeMirror,wingify/CodeMirror,thomasjm/CodeMirror,nightwing/CodeMirror,mtaran-google/CodeMirror,mtaran-google/CodeMirror,hackmdio/CodeMirror,thomasjm/CodeMirror,SidPresse/CodeMirror,SidPresse/CodeMirror