BUG - Slide up in very small steps >> NavBar does not appear

**Describe the bug**
If you scroll up without having your finger on the screen, the navbar is not displayed when you arrive at the top **OR** slide up in very small steps

**To Reproduce**
Steps to reproduce the behavior:
1. Open the Demo.
2. Scroll up without finger like in the video.
3. NavBar does not appear

**Expected behavior**
NavBar should at appear when you arrive at the top (or before)

**Video (ZIP)**
[ScreenRecording_10-12-2018 00-53-41.MP4.zip](https://github.com/andreamazz/AMScrollingNavbar/files/2470982/ScreenRecording_10-12-2018.00-53-41.MP4.zip)

On the 3rd try you can see that the NavBar does not appear.