Issue with continuous scrolling using (macOs + Safari) trackpad

[Reshmi123]

This issue is a Bug.

Related issue : #338

Pull request: None

Expected Behaviour
should Scroll up and down smoothly and continuously using trackpad.

Observed behaviour
Scroll up ok but scroll down locked.

Steps to reproduce

1.Open epub with Safari 11.1.1 : https://readium.firebaseapp.com/?epub=epub_content%2Faccessible_epub_3&
Similar kind of issue is reproducing in our case but we can not share the link due copyrights

2.Change the Settings of Scroll Mode to Continuous

3.On the book, cannot scroll down.

Product

Readium version: 0.8.0
Safari: 11.1.1
macOS: High Sierra (version: 10.13.5)

Additional information

Chrome + macOS + Continuous Scroll Mode = OK
Firefox + macOS + Continuous Scroll Mode = OK
Edge + Windows 10 + Continuous Scroll Mode = OK