Small typo fix in file_record.html (#2)

Typo exension → extension

Author: Naheulf

concepts/file_record.html

@@ -204,7 +204,7 @@ <h2>Layout</h2>
           </tr>
           <tr>
             <td class="numeric">0x04</td>
-            <td>Record is an exension (Set for records in the $Extend directory)</td>
+            <td>Record is an extension (Set for records in the $Extend directory)</td>
           </tr>
           <tr>
             <td class="numeric">0x08</td>