add random string function

lib/diskuy/utility/utility.ex

@@ -3,4 +3,10 @@ defmodule Diskuy.Utility.Utility do
     text_list = String.split(text, " ", trim: true)
     Enum.map_join(text_list, " ", &String.capitalize/1)
   end
+
+  @spec random_string(non_neg_integer) :: binary
+  def random_string(length) do
+    :crypto.strong_rand_bytes(length) |> Base.encode64 |> binary_part(0, length)
+  end
+
 end