Version bump to 4.0.0

Author: darrenklein

README.md

@@ -12,7 +12,7 @@ The package can be installed by adding `ex_aws_dynamo` to your list of dependenc
 ```elixir
 def deps do
   [
-    {:ex_aws_dynamo, "~> 3.0"},
+    {:ex_aws_dynamo, "~> 4.0"},
     {:jason, "~> 1.0"},
     {:hackney, "~> 1.9"}
   ]

mix.exs

@@ -1,7 +1,7 @@
 defmodule ExAws.Dynamo.Mixfile do
   use Mix.Project
 
-  @version "3.0.3"
+  @version "4.0.0"
   @service "dynamo"
   @url "https://github.com/ex-aws/ex_aws_#{@service}"
   @name __MODULE__ |> Module.split() |> Enum.take(2) |> Enum.join(".")