Ensure recursive copy takes into account the proper target directory

Author: José Valim

lib/mix/lib/mix/utils.ex

@@ -343,7 +343,7 @@ defmodule Mix.Utils do
     symlink_source = make_relative_path(source, target)
     case :file.make_symlink(symlink_source, target) do
       :ok -> :ok
-      { :error, _ } -> File.cp_r!(source, Path.join(target, "."))
+      { :error, _ } -> File.cp_r!(source, Path.dirname(target))
     end
   end