Bump csharp version

csharp/src/Google.Protobuf/Google.Protobuf.csproj

@@ -4,7 +4,7 @@
     <Description>C# runtime library for Protocol Buffers - Google's data interchange format.</Description>
     <Copyright>Copyright 2015, Google Inc.</Copyright>
     <AssemblyTitle>Google Protocol Buffers</AssemblyTitle>
-    <VersionPrefix>3.3.0</VersionPrefix>
+    <VersionPrefix>3.4.0</VersionPrefix>
     <Authors>Google Inc.</Authors>
     <TargetFrameworks>netstandard1.0;net451</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>