corrects file name for the Docker file

Author: nickfloyd

.devcontainer/Docker renamed to .devcontainer/Dockerfile

@@ -6,6 +6,3 @@ FROM mcr.microsoft.com/vscode/devcontainers/dotnet
 # "install" the dotnet 3.1 & 6.0 runtime for tests
 COPY --from=mcr.microsoft.com/dotnet/sdk:3.1 /usr/share/dotnet/shared /usr/share/dotnet/shared
 COPY --from=mcr.microsoft.com/dotnet/sdk:6.0 /usr/share/dotnet/shared /usr/share/dotnet/shared
-
-# Add mono complete for omnisharp
-RUN apt-get install -y mono-complete