Fix right clicks triggers native context menu on macOS (#38)

Also reported here mhutchie#870

Author: ipcjs

web/contextMenu.ts

@@ -100,6 +100,11 @@ class ContextMenu {
 			e.stopPropagation();
 		});
 
+		menu.addEventListener('contextmenu', (e) => {
+			// The user right-clicked on the context menu => keep the context menu open
+			e.stopPropagation();
+		});
+
 		this.target = target;
 		if (this.target !== null && this.target.type !== TargetType.Repo) {
 			alterClass(this.target.elem, CLASS_CONTEXT_MENU_ACTIVE, true);