Update travis to clang-3.9 (#177)
Update travis to clang-3.9 (#177)

This should have been done in PR #150

I'm getting some odd failures about clang-3.9 missing which I hadn't seen before.
GoogleCloudPlatform/google-cloud-dotnet-debugger,GoogleCloudPlatform/google-cloud-dotnet-debugger,GoogleCloudPlatform/google-cloud-dotnet-debugger,GoogleCloudPlatform/google-cloud-dotnet-debugger