fix(Example): Add missing import for catch operator (#409)

docs/effects/README.md

@@ -42,6 +42,7 @@ want to use to perform a side effect.
 // ./effects/auth.ts
 import 'rxjs/add/operator/map';
 import 'rxjs/add/operator/mergeMap';
+import 'rxjs/add/operator/catch';
 import { Injectable } from '@angular/core';
 import { Http } from '@angular/http';
 import { Observable } from 'rxjs/Observable';