Bump version to 1.6.3

Author: mathieuprog

README.md

@@ -217,7 +217,7 @@ Add `polymorphic_embed` for Elixir as a dependency in your `mix.exs` file:
 ```elixir
 def deps do
   [
-    {:polymorphic_embed, "~> 1.6.2"}
+    {:polymorphic_embed, "~> 1.6.3"}
   ]
 end
 ```

mix.exs

@@ -1,7 +1,7 @@
 defmodule PolymorphicEmbed.MixProject do
   use Mix.Project
 
-  @version "1.6.2"
+  @version "1.6.3"
 
   def project do
     [