message: docs: Update loopback docs
diff: Loopback
  ========
  +If you're using Loopback 2.x LTS, make sure
  +you've migrated to `strong-error-handler
  +<https://loopback.io/doc/en/lb2/Using-strong-error-handler.html>`_, otherwise no
  +errors will get to ``raven-node``.
  +
  +Configure ``raven-node`` as early as possible:
  +
  .. code-block:: javascript
  - // server/middleware/sentry.js
  + // server/server.js
  - var Raven = require('raven');
  + const Raven = require('raven');
  Raven.config('__DSN__').install();
  - module.exports = function () {
  - return Raven.errorHandler();
  - }
  +Add ``Raven.errorHandler`` as a Loopback middleware:
  -.. code-block:: javascript
  +.. code-block:: json
  // server/middleware.json
  - "final": {
  - "./middleware/sentry": {}
  + "final:after": {
  + "raven#errorHandler": {},
  + "strong-error-handler": {
  + "debug": false,
  + "log": false
  + }
  }
  +
  +You're all set!
  