Possible fix for #154 - UV channel was not being serialized

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/UVMaterialSlot.cs

     [Serializable]
     public class UVMaterialSlot : Vector2MaterialSlot, IMayRequireMeshUV
     {
-        private UVChannel m_Channel = UVChannel.UV0;
+        [SerializeField]
+        UVChannel m_Channel = UVChannel.UV0;
 
         public UVChannel channel
         {