fix(docsApp): make Dropdown#onToggle binding optional

Author: caitp

docs/app/assets/js/angular-bootstrap/dropdown-toggle.js

@@ -93,7 +93,7 @@ angular.module('ui.bootstrap.dropdown', [])
       dropdownService.close( $scope );
     }
 
-    $scope.onToggle({ open: !!value });
+    if ($scope.onToggle) $scope.onToggle({ open: !!value });
   });
 
   $scope.$on('$locationChangeSuccess', function() {
@@ -107,7 +107,7 @@ angular.module('ui.bootstrap.dropdown', [])
     controller: 'DropdownController',
     scope: {
       isOpen: '=?',
-      onToggle: '&'
+      onToggle: '&?'
     },
     link: function(scope, element, attrs, dropdownCtrl) {
       dropdownCtrl.init( element );
@@ -142,4 +142,4 @@ angular.module('ui.bootstrap.dropdown', [])
       });
     }
   };
-});
+});