Corrected shouldBeConsumedByChild logic for vertical scrolling

[tibineagu]

Fixes mdbootstrap/perfect-scrollbar#139

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• [x] Read CONTRIBUTING.md
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  • addressed in tagged issue
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Description

Because deltaY is negative when the user is scrolling down, the logic in shouldBeConsumedByChild for vertical scrolling was flawed.

The solution was simply adjusting the > / < operators to match the deltaY values.

[tibineagu]

@filipkappa @marveluck @mdbootstrap any feedback or ETA for this being integrated?