Editorial: fix grammar in note about error checking serialization

Author: shannonbooth

source

@@ -94337,7 +94337,7 @@ interface <dfn interface>NavigationHistoryEntry</dfn> : <span>EventTarget</span>
     return an <span data-x="navigation-api-early-error-result">early error result</span> for that
     exception.</p>
 
-    <p class="note">It is importantly to perform this step early, since serialization can invoke web
+    <p class="note">It is important to perform this step early, since serialization can invoke web
     developer code, which in turn might change various things we check in later steps.</p>
    </li>
 
@@ -94418,7 +94418,7 @@ interface <dfn interface>NavigationHistoryEntry</dfn> : <span>EventTarget</span>
     return an <span data-x="navigation-api-early-error-result">early error result</span> for that
     exception.</p>
 
-    <p class="note">It is importantly to perform this step early, since serialization can invoke web
+    <p class="note">It is important to perform this step early, since serialization can invoke web
     developer code, which in turn might change various things we check in later steps.</p>
    </li>