Build error fix.

UnitTests/UnitTests.UWP/UnitTests.UWP.csproj

@@ -245,6 +245,10 @@
       <Project>{b1e850ff-dde6-44d5-a830-34250e97a687}</Project>
       <Name>Microsoft.Toolkit.Uwp.Connectivity</Name>
     </ProjectReference>
+    <ProjectReference Include="..\..\Microsoft.Toolkit.Uwp.UI.Animations\Microsoft.Toolkit.Uwp.UI.Animations.csproj">
+      <Project>{b24a296c-b3eb-4e06-a64e-74ac2d1acc91}</Project>
+      <Name>Microsoft.Toolkit.Uwp.UI.Animations</Name>
+    </ProjectReference>
     <ProjectReference Include="..\..\Microsoft.Toolkit.Uwp.UI.Controls\Microsoft.Toolkit.Uwp.UI.Controls.csproj">
       <Project>{e9faabfb-d726-42c1-83c1-cb46a29fea81}</Project>
       <Name>Microsoft.Toolkit.Uwp.UI.Controls</Name>