[unity] Fix UI TintBlack shader.

spine-unity/Assets/spine-unity/Modules/SkeletonGraphic/Shaders/Spine-SkeletonGraphic-TintBlack.shader

@@ -110,9 +110,9 @@ Shader "Spine/SkeletonGraphic Tint Black (Premultiply Alpha)"
 				clip (texColor.a - 0.001);
 				#endif
 
-				return (texColor * IN.color) + float4(((1-texColor.rgb) * (_Black.rgb + float3(IN.uv1.r, IN.uv1.g, IN.uv2.r)) * texColor.a*_Color.a*i.vertexColor.a), 0);
+				return (texColor * IN.color) + float4(((1-texColor.rgb) * (_Black.rgb + float3(IN.uv1.r, IN.uv1.g, IN.uv2.r)) * texColor.a * _Color.a * IN.color.a), 0);
 			}
 		ENDCG
 		}
 	}
-}
+}