build: allow for rxjs v7 usage (#1359)

Author: CaerusKaru

src/lib/package.json

@@ -30,7 +30,7 @@
     "@angular/core": "0.0.0-NG",
     "@angular/common": "0.0.0-NG",
     "@angular/platform-browser": "0.0.0-NG",
-    "rxjs": "^6.0.0"
+    "rxjs": "^6.0.0 || ^7.0.0"
   },
   "sideEffects": false
 }