timepicker's show-spinners are not being dynamically updated

[Silverium]

Bug description:

Assigning a variable, like $scope.myBool to the attribute show-spinners only grants the rendering once. It's not updated when the variable changes its value.

Link to minimally-working plunker that reproduces the issue:

https://plnkr.co/edit/aOPIv0XuxNT77NEJcaz0?p=preview

Steps to reproduce the issue:

Click on green button toggle myBool and you will see that show-meridian="myBool" is working, while show-spinners="myBool" is not.

Version of Angular, UIBS, and Bootstrap

Angular: 1.6.1

UIBS: 2.5.0

Bootstrap: 3.3.7