Bump rxjs from 6.4.0 to 6.6.7

Bumps [rxjs](https://github.com/reactivex/rxjs) from 6.4.0 to 6.6.7.
- [Release notes](https://github.com/reactivex/rxjs/releases)
- [Changelog](https://github.com/ReactiveX/rxjs/blob/6.6.7/CHANGELOG.md)
- [Commits](ReactiveX/rxjs@6.4.0...6.6.7)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

package-lock.json

@@ -21,7 +21,7 @@
     "@angular/platform-browser-dynamic": "~8.2.4",
     "@angular/router": "~8.2.4",
     "@uirouter/angular": "^5.0.0",
-    "rxjs": "~6.4.0",
+    "rxjs": "~6.6.7",
     "tslib": "^1.10.0",
     "zone.js": "~0.9.1"
   },