Scroll broken when zoom <> 100%

[rychoo2]

Scrolling isn't working when browser zoom is different than 100%.
To reproduce,

1. go to the demo page:
   http://nolanus.github.io/ng2-page-scroll/simple
2. change browser zoom ctrl[+/-]
3. click Start
   Issue observed on chrome and safari

[Nolanus]

Thanks for the bug report, I'll have a look into this.
Symptoms look similar like for #37

[rychoo2]

Thanks. Must be something with handling animation. Works fine when no animation:
PageScrollConfig.defaultDuration = 0;