fix(AgmMarkerCluster): fixes info windows

the marker cluster needs it's own `InfoWindowManager`, otherwise
`InfoWindowManager` would be injected with the root `MarkerManager`
instead of the `ClusterManager`

fixes #1126

packages/js-marker-clusterer/directives/marker-cluster.ts

@@ -1,7 +1,7 @@
 import {Directive, Input, OnDestroy, OnChanges, OnInit, SimpleChange} from '@angular/core';
 
 import {ClusterManager} from '../services/managers/cluster-manager';
-import {MarkerManager} from '@agm/core';
+import {MarkerManager, InfoWindowManager} from '@agm/core';
 
 import {ClusterOptions, ClusterStyle} from '../services/google-clusterer-types';
 
@@ -34,7 +34,11 @@ import {ClusterOptions, ClusterStyle} from '../services/google-clusterer-types';
  */
 @Directive({
   selector: 'agm-marker-cluster',
-  providers: [ClusterManager, {provide: MarkerManager, useExisting: ClusterManager}]
+  providers: [
+    ClusterManager,
+    {provide: MarkerManager, useExisting: ClusterManager},
+    InfoWindowManager,
+  ]
 })
 export class AgmMarkerCluster implements OnDestroy, OnChanges, OnInit, ClusterOptions {
   /**