Include project.clj by default for lein plugin

Since the file project.clj is specific to Leiningen projects it seem
like a good default.

Fixes: #279

Author: jacobemcken

lein-cljfmt/src/leiningen/cljfmt.clj

@@ -10,7 +10,8 @@
     (if (empty? paths)
       (leiningen.core.main/abort "No source or test paths defined in project map")
       (->> (map io/file paths)
-           (filter #(and (.exists %) (.isDirectory %)))))))
+           (filter #(and (.exists %) (.isDirectory %)))
+           (cons "project.clj")))))
 
 (defn- execute-command [command options paths]
   (case command