false negative: no-internal-module

[unional]

https://github.com/typed-typings/npm-chai/blob/master/lib/Chai.d.ts#L28-L33

/* tslint:disable:no-internal-module */
declare global {
  interface Object {
    should: A.Assertion;
  }
}

Global augmentation is detected as internal module.

[jkillian]

For context, this is a fairly new feature of TypeScript: microsoft/TypeScript#6213