Update SignalR extension version to 1.5.0 (#165)

Author: Y-Sindo

samples/BidirectionChat/csharp/extensions.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>	
   <ItemGroup>	
     <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="3.0.3" />	
-    <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.SignalRService" Version="1.2.2" />	
+    <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.SignalRService" Version="1.5.0" />	
   </ItemGroup>	
   <ItemGroup>	
     <None Update="content/index.html">