fixed the package version issue of Live chat sample

Author: kerryjiang

Directory.Packages.props

@@ -24,5 +24,6 @@
     <PackageVersion Include="xunit" Version="2.4.0" />    
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.4.0" />
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="8.0.0" />
+    <PackageVersion Include="Microsoft.AspNetCore.SpaServices.Extensions" Version="3.1.5" />
   </ItemGroup>
 </Project>

samples/LiveChat/LiveChat.csproj

@@ -17,7 +17,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.SpaServices.Extensions" Version="3.1.5" />
+    <PackageReference Include="Microsoft.AspNetCore.SpaServices.Extensions" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="..\..\assets\supersocket.pfx">