Add Story Endpoint to Endpoints module declaration

While attempting to call ```.story([id])``` on a project object, received error:

> NameError: uninitialized constant Tracker::Endpoints::Story

Found we weren't actually including that endpoint. =)
Merge pull request #5 from adimasuhid/master

Adds Eagerloading Tasks in Story
Updated the exception message.
Merge pull request #6 from BFGeorge9000/patch-1

Add Story Endpoint to Endpoints module declaration
Skip rbx for now. Travis error: rbx is not installed.
Release 0.2.3
Adds Tasks Endpoint to Story