Merge pull request #4094 from tuvistavie/update_deps_clean_doc

Add deps.clean --build documentation.

Author: josevalim

lib/mix/lib/mix/tasks/deps.clean.ex

@@ -15,6 +15,7 @@ defmodule Mix.Tasks.Deps.Clean do
     * `--unused`   - deletes only unused dependencies (no longer mentioned
       in the `mix.exs` file)
     * `--unlock`   - also unlocks the deleted dependencies
+    * `--build`    - deletes only dependencies compiled files (keep the source files)
 
   By default this task works across all environments, unless `--only`
   is given.