Update to [email protected].

Main changes:

* ES6ify a few classes.
* Fix issue when calling `.replaceWith` when the current transition is also
  a `.replaceWith` (previously this would surprisingly result in a
  `.transitionTo` _not_ a replace).

[Full
changelog](tildeio/router.js@v2.0.0-beta.1...v2.0.0-beta.2)

package.json

@@ -120,7 +120,7 @@
     "puppeteer": "^0.13.0",
     "qunit": "^2.5.0",
     "route-recognizer": "^0.3.3",
-    "router_js": "^2.0.0-beta.1",
+    "router_js": "^2.0.0-beta.2",
     "rsvp": "^4.8.0",
     "semver": "^5.5.0",
     "serve-static": "^1.12.2",