can't debug netcore 3 on debian linux (buster)

## Environment data
`dotnet --info` output:
```
.NET Core SDK (reflecting any global.json):
Version: 3.0.100-preview-009812
Commit: e3abf6e935

Runtime Environment:
OS Name: debian
OS Version:
OS Platform: Linux
RID: debian-x64
Base Path: /usr/share/dotnet/sdk/3.0.100-preview-009812/

Host (useful for support):
Version: 3.0.0-preview-27122-01
Commit: 00c5c8bc40

.NET Core SDKs installed:
3.0.100-preview-009812 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.App 3.0.0-preview-18579-0056 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.0.0-preview-27122-01 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download
```
VS Code version:
C# Extension version: 1.17.1

## Steps to reproduce
1. Add breakpoint
1. Start debugging

## Expected behavior
stop on break

## Actual behavior
Debug adapter process has terminated unexpectedly (exit code: null)