[bug report] Does not work with Angular 9.1.0

[ghost]

REQUIRED: Before filing a bug report

Change each [ ] to [x] when you have done it.

• My issue title starts with [bug report]
• I have read the README, especially the 'classic blunders' section, and the dragula docs.
• I have searched through the ng2-dragula issues for related problems, including closed issues.
• I have browsed through the issues labeled "future reference" for problems that have been solved before or have a known workaround.
• I am using the latest version of ng2-dragula.

Describe the bug (required)

After updating Angular to version 9.1.0, ng2-dragula does not work. I'm getting error:

main.8c80991e3673d847bd30.js:1 ERROR Error: Uncaught (in promise): ReferenceError: dragulaExpt__default is not defined
ReferenceError: dragulaExpt__default is not defined

Error points to file /node_modules/ng2-dragula/dist/fesm2015/ng2-dragula.js, line 2

import dragulaExpt__default, {  } from 'dragula';

The error happens only in runtime in a production build (ng build --prod).

[ghost]

angular/angular-cli#17320