Add v3 back to mix.exs (#11)

* Fix basic shortuuid v4 support (#10)

* re-add v3

* update readme

Author: gpedic

README.md

@@ -52,7 +52,7 @@ by adding `ecto_shortuuid` to your list of dependencies in `mix.exs`:
 ```elixir
 def deps do
   [
-    {:ecto_shortuuid, "~> 0.2"}
+    {:ecto_shortuuid, "~> 0.3.0"}
   ]
 end
 ```

mix.exs

@@ -67,7 +67,7 @@ defmodule Ecto.ShortUUID.MixProject do
       {:credo, "~> 1.7", only: [:dev, :test], runtime: false},
       {:excoveralls, "~> 0.16.1", only: :test, runtime: false},
       {:benchfella, "~> 0.3.5", only: [:dev, :test]},
-      {:shortuuid, "~> 2.1 or ~> 4.0"},
+      {:shortuuid, "~> 4.0 or ~> 3.0 or ~> 2.1"},
       {:ecto, "~> 2.2 or ~> 3.0"}
     ]
   end