fix(core): update

ts/smartrx.plugins.rxjs.ts

@@ -1,6 +1,8 @@
 // this file is intended to keep the bundle size down
 
-export { Observable, Subject, fromEvent, ReplaySubject, Subscription, Observer } from 'rxjs';
+export { Observable, Subject, fromEvent, ReplaySubject, Subscription } from 'rxjs';
+
+export type { Observer } from 'rxjs';
 
 import { startWith, takeUntil, map, debounce, debounceTime } from 'rxjs/operators';