Add `.default` in `extenstion.ts`. I feel like I shouldn't need to do this. I am using tsc 3.1.1.
Add `.default` in `extenstion.ts`.
I feel like I shouldn't need to do this. I am using tsc 3.1.1.

leanprover/vscode-lean,leanprover/vscode-lean,leanprover/vscode-lean