feat: update RxJS peer dependency to 5.0.0-rc.4

Closes #13125

RxJS from beta-12 to rc.4, has removed the `cache`
operator. (See https://github.com/ReactiveX/rxjs/blob/master/CHANGELOG.md#breaking-changes-1)
If your application relies on it, then we suggest 
that you use the one from this gist:
https://gist.github.com/robwormald/19dea0c70a6e01aadced6731aed4f9f7

modules/rollup-test/package.json

@@ -23,7 +23,7 @@
     "rollup-plugin-node-resolve": "^1.5.0",
     "rollup-plugin-typescript": "^0.7.3",
     "rollup-plugin-uglify": "^0.3.1",
-    "rxjs-es": "^5.0.0-beta.12",
+    "rxjs-es": "^5.0.0-rc.4",
     "typescript": "^1.9.0-dev.20160423",
     "uglify-js": "^2.6.2"
   },