feat(@schematics/angular): update scaffolding rxjs version to 6.5.1

Author: Alan Agius

packages/schematics/angular/utility/latest-versions.ts

@@ -9,7 +9,7 @@
 export const latestVersions = {
   // These versions should be kept up to date with latest Angular peer dependencies.
   Angular: '~8.0.0-beta.12',
-  RxJs: '~6.4.0',
+  RxJs: '~6.5.1',
   ZoneJs: '~0.9.0',
   TypeScript: '~3.4.3',
   TsLib: '^1.9.0',