Change description of get in options manager

Co-authored-by: Athan <kgryte@gmail.com>

src/generators/notebook/options_manager.ts

@@ -99,7 +99,7 @@ class OptionsManager extends Registry.IOptionsManager {
   }
 
   /**
-   * Gets ToC configuration of whether to enable collapsible cells
+   * Gets the ToC setting specifying whether to allow collapsing notebook cells.
    */
   get collapsibleNotebooks() {
     return this._collapsible;