API signature is not shown for complex signatures

**I'm submitting a bug report**

* **Browser:**
Chrome 62 | Firefox 57

**Current behavior:**
In the API docs on http://aurelia.io complex signatures are not displayed.

**Expected/desired behavior:**
* **What is the expected behavior?**
For example on http://aurelia.io/docs/api/fetch-client/interface/Interceptor/property/request the return signature should be `Request | Response | Promise` and on http://aurelia.io/docs/api/router/interface/RoutableComponentActivate/method/activate it should be `Promise | PromiseLike | IObservable | void`.

* **What is the motivation / use case for changing the behavior?**
Accurate type definitions.

Start with the two API documentation pages named in the report: the Interceptor request property and RoutableComponentActivate activate method. Compare their displayed signatures with the expected return types in the issue, then trace the documentation generation or rendering path that produces those pages. Done means both complex signatures are shown accurately.

Written by the indexing model from the issue text.