[api-documenter] Properties with function values are not recognized as functions

[fhinkel]

When a class function is defined as a class property rather than a method, it's description lacks the parameters.docfx then renders it as a property without params or parentheses.

Property with function value:

createReadStream: () => Readable;

Same function defined as method:

createReadStream(): Readable {
  return new Readable();
}

The first gets rendered as in the pic when it should be createdReadStream() analogous to the methods further down.