chore: use function instead of lambda

src/index.ts

@@ -1,4 +1,4 @@
-export { NgSelectComponent, NG_SELECT_DEFAULT_CONFIG } from './ng-select/ng-select.component';
+export { NgSelectComponent, NG_SELECT_DEFAULT_CONFIG, SELECTION_MODEL_FACTORY } from './ng-select/ng-select.component';
 export { NgSelectModule } from './ng-select/ng-select.module';
 export { NgOption, NgSelectConfig } from './ng-select/ng-select.types';
 export { SelectionModel } from './ng-select/selection-model';

src/ng-select/ng-select.module.ts

@@ -16,7 +16,7 @@ import {
 import { NgOptionComponent } from './ng-option.component';
 import { NgOptionHighlightDirective } from './ng-option-highlight.directive';
 import { NgDropdownPanelComponent } from './ng-dropdown-panel.component';
-import { DefaultSelectionModel } from './selection-model';
+import { DefaultSelectionModelFactory } from './selection-model';
 
 @NgModule({
     declarations: [
@@ -54,7 +54,7 @@ import { DefaultSelectionModel } from './selection-model';
         NgTagTemplateDirective
     ],
     providers: [
-        { provide: SELECTION_MODEL_FACTORY, useValue: () => new DefaultSelectionModel() },
+        { provide: SELECTION_MODEL_FACTORY, useValue: DefaultSelectionModelFactory },
         {
             provide: NG_SELECT_DEFAULT_CONFIG,
             useValue: {

src/ng-select/selection-model.ts

@@ -2,6 +2,10 @@ import { NgOption } from './ng-select.types';
 
 export type SelectionModelFactory = () => SelectionModel;
 
+export function DefaultSelectionModelFactory() {
+    return new DefaultSelectionModel();
+}
+
 export interface SelectionModel {
     value: NgOption[];
     select(item: NgOption, multiple: boolean, selectableGroupAsModel: boolean);