title: Ngx-Bootstrap and Angular 9 ModuleWithProviders Error
body: <p>I get the error below</p>
  
  <pre><code>ERROR in node_modules/ngx-bootstrap/popover/popover.module.d.ts:3:23 - error NG6005: 
  PopoverModule.forRoot returns a ModuleWithProviders type without a generic type argument. 
  Please add a generic type argument to the ModuleWithProviders type.
  If this occurrence is in library code you don't control, please contact the library authors.
  </code></pre>
  
  <p>I just added Ngx-Bootstrap's Popover Module and imported <code>PopoverModule.forRoot()</code>. This seems to be Angular 9 incompatibility. How to solve this? </p>