Fixed small typos and dates.

src/PackageInfo.props

@@ -4,7 +4,7 @@
   <PropertyGroup>
     
     <Authors>Vicente Penades</Authors>
-    <Copyright>Copyright (c) 2019 Vicente Penades</Copyright>
+    <Copyright>Copyright (c) 2020 Vicente Penades</Copyright>
     <Description>SharpGLTF is a C# library for reading and writing glTF2 3D models</Description>
     
     <RepositoryUrl>https://github.com/vpenades/SharpGLTF</RepositoryUrl>

src/SharpGLTF.Toolkit/Geometry/VertexBuilder.cs

@@ -212,9 +212,9 @@ namespace SharpGLTF.Geometry
             return new VertexBuilder<TvG, TvM, TvS>(tuple.Geo, tuple.Mat);
         }
 
-        public static implicit operator VertexBuilder<TvG, TvM, TvS>((TvG Geo, TvS Mat) tuple)
+        public static implicit operator VertexBuilder<TvG, TvM, TvS>((TvG Geo, TvS Skin) tuple)
         {
-            return new VertexBuilder<TvG, TvM, TvS>(tuple.Geo, tuple.Mat);
+            return new VertexBuilder<TvG, TvM, TvS>(tuple.Geo, tuple.Skin);
         }
 
         public static implicit operator VertexBuilder<TvG, TvM, TvS>(TvG g)