make sure output dir exists

Author: andyleclair

.gitignore

@@ -27,4 +27,4 @@ personal-*.tar
 
 .expert
 
-output/
+output/*

lib/mix/tasks/copy_static.ex

@@ -7,6 +7,7 @@ defmodule Mix.Tasks.CopyStatic do
   def run(_args) do
     Mix.shell().info([:green, "Copying static files"])
 
+    File.mkdir(@output_dir)
     File.cp_r!(@font_dir, Path.join([@output_dir, "assets", "fonts"]))
     File.cp_r!(@image_dir, Path.join([@output_dir, "assets", "images"]))
   end