fix(package): update @ng-bootstrap/ng-bootstrap to version 5.2.1

Closes #54

Author: greenkeeper[bot]

demo/package.json

@@ -39,7 +39,7 @@
     "@angular/platform-browser-dynamic": "^7.2.8",
     "@angular/platform-server": "^7.2.8",
     "@angular/router": "^7.2.8",
-    "@ng-bootstrap/ng-bootstrap": "^4.1.0",
+    "@ng-bootstrap/ng-bootstrap": "^5.2.1",
     "@stackblitz/sdk": "^1.3.0",
     "bootstrap": "^4.3.1",
     "core-js": "^2.6.5",