build: update to angular-v9.1.12 (#1215)

Fixes: #1216

src/app/groups/groups-view/group-actions/group-attendance/group-attendance.component.ts

@@ -1,6 +1,6 @@
 /** Angular Imports */
 import { Component, OnInit } from '@angular/core';
-import { MatDialog } from '@angular/material';
+import { MatDialog } from '@angular/material/dialog';
 import { DatePipe } from '@angular/common';
 import { ActivatedRoute, Router } from '@angular/router';
 import { FormControl } from '@angular/forms';

src/app/groups/groups-view/group-actions/manage-group-members/manage-group-members.component.ts

@@ -9,7 +9,7 @@ import { DeleteDialogComponent } from 'app/shared/delete-dialog/delete-dialog.co
 /** Custom Services */
 import { GroupsService } from 'app/groups/groups.service';
 import { ClientsService } from 'app/clients/clients.service';
-import { MatDialog } from '@angular/material';
+import { MatDialog } from '@angular/material/dialog';
 
 /**
  * Manage Group Members Component