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

scripts/ci-lite/offline_compiler_test.sh

@@ -10,7 +10,7 @@ PKGS=(
   reflect-metadata@0.1.8
   typescript@2.0.2
   zone.js@0.6.25
-  rxjs@5.0.0-beta.12
+  rxjs@5.0.0-rc.4
   @types/{node@6.0.38,jasmine@2.2.33}
   jasmine@2.4.1
   webpack@2.1.0-beta.21