upgrade C# to protobuf 3.3.0
diff --git a/src/csharp/Grpc.Core/Version.csproj.include b/src/csharp/Grpc.Core/Version.csproj.include
index 6af2af1..8388bfd 100755
--- a/src/csharp/Grpc.Core/Version.csproj.include
+++ b/src/csharp/Grpc.Core/Version.csproj.include
@@ -2,6 +2,6 @@
 <Project>
   <PropertyGroup>
     <GrpcCsharpVersion>1.4.0-dev</GrpcCsharpVersion>
-    <GoogleProtobufVersion>3.2.0</GoogleProtobufVersion>
+    <GoogleProtobufVersion>3.3.0</GoogleProtobufVersion>
   </PropertyGroup>
 </Project>