Issue Type: Bug

When trying to augment an interface contained in a module, the Organize Imports option of VSCode removed the required import.

Sample code:

import { Caseless } from 'caseless';

declare module 'caseless' {
  interface Caseless {
    test(name: KeyType): boolean;
  }
}

When you save, Organize Imports removes the import so the augmentation doesn't happen.

VS Code version: Code 1.33.1 (51b0b28134d51361cf996d2f0a1c698247aeabd8, 2019-04-11T08:22:55.268Z)
OS version: Darwin x64 18.5.0