Add type definition for test helper import

[chriskrycho]

Resolves typed-ember/ember-cli-typescript#983

[richard-viney]

In testing [email protected] it doesn't appear to actually include the new type definitions in the package, i.e. node_modules/ember-cli-htmlbars/index.d.ts doesn't exist after installing with yarn.

Inspecting the contents of https://registry.npmjs.org/ember-cli-htmlbars/-/ember-cli-htmlbars-4.3.0.tgz also shows no type definitions are present.

[chriskrycho]

Doh! That would be because the files key in package.json only specifies lib, I believe. Should be an easy and quick fix; I’ll have a PR up in an hour or so.

[rwjblue]

Fixed in #494

[chriskrycho]

SNIPED!