Bump version to v0.3.1

Author: sheharyarn

README.md

@@ -63,7 +63,7 @@ Add `:memento` to your list of dependencies in your Mix file:
 
 ```elixir
 def deps do
-  [{:memento, "~> 0.3.0"}]
+  [{:memento, "~> 0.3.1"}]
 end
 ```
 

mix.exs

@@ -3,7 +3,7 @@ defmodule Memento.Mixfile do
 
   @app     :memento
   @name    "Memento"
-  @version "0.3.0"
+  @version "0.3.1"
   @github  "https://github.com/sheharyarn/#{@app}"
   @author  "Sheharyar Naseer"
   @license "MIT"