Recommend latest version in README (#39)

README.md

@@ -11,7 +11,7 @@ You can use plug_crypto in your projects by adding it to your `mix.exs` dependen
 
 ```elixir
 def deps do
-  [{:plug_crypto, "~> 1.0"}]
+  [{:plug_crypto, "~> 2.0"}]
 end
 ```