upgrade Grpc.sln to newest Google.Protobuf nuget

src/csharp/Grpc.Examples.Tests/Grpc.Examples.Tests.csproj

src/csharp/Grpc.Examples.Tests/packages.config

src/csharp/Grpc.Examples/Grpc.Examples.csproj

src/csharp/Grpc.Examples/packages.config

...harp/Grpc.HealthCheck.Tests/Grpc.HealthCheck.Tests.csproj

src/csharp/Grpc.HealthCheck.Tests/packages.config

src/csharp/Grpc.HealthCheck/Grpc.HealthCheck.csproj

src/csharp/Grpc.HealthCheck/packages.config

...rp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj

src/csharp/Grpc.IntegrationTesting/packages.config