title: Warning from ngrx about runtime checks
body: <p>I upgraded my app from Angular 7 to Angular 8 using <code>ng update</code>. When I run it via <code>ng serve</code>, There's a warning printed in my console from <code>ngrx</code>:</p>
  
  <pre><code>@ngrx/store: runtime checks are currently opt-in but will be the default in the next major version with the possibility to opt-out, see https://ngrx.io/guide/migration/v8 for more information.
  </code></pre>
  
  <p>The documentation at the provided link talks about <code>ngrx-store-freeze</code> being deprecated. However, my application does not use <code>ngrx-store-freeze</code>, and I have no idea what a "runtime check" is. What do I need to change in my code to address the source of this warning?</p>