Merdian based timepicker - flips back to AM when hour is manually entered

[k-schneider]

Bug description:

When a timepicker has merdian set to true, and the hour is manually typed by the user the PM will automatically switch back to AM. I wouldn't expect this to happen and can easily be overlooked by a user who was doing a simple hour change (ie 6:00PM to 7:00PM).

Link to minimally-working plunker that reproduces the issue:

This behavior can be observed on the timepicker demo page.
https://ng-bootstrap.github.io/#/components/timepicker

Version of Angular, ng-bootstrap, and Bootstrap:

Angular: 4.x

ng-bootstrap: 1.0.0-alpha.26

Bootstrap: v4.0.0-alpha.6