uncatchable TaskCancelation

0.7.0

• within a task generator function, TaskCancelation "errors" are
  longer "catchable" in the catch block of a try/catch. This means
  you no longer have to check if the error thrown is a cancelation
  in order to handle it differently than an exception.
• That said, since promises have no concept of cancelation, if
  you perform a task within a promise (or you call
  someTask.perform().then(...).catch(...)), then any promise
  catch handlers will be called with TaskCancelation "errors",
  and if you need to distinguish between cancelation and exceptions
  thrown, you can import and use the new didCancel utility function,
  which returns true if the error passed to it is a TaskCancelation.
  Previously, the only safe way to test this was to check
  err && err.name === 'TaskCancelation'; now you can just
  import { didCancel } from 'ember-concurrency' and
  check didCancel(err).