Fixes #21 Event scroll bottom issue

[saba-ja]

Originating Project/Creator	F' GDS 2.0
Affected Component	event.js
Affected Architectures(s)	NA
Related Issue(s)	#21
Has Unit Tests (y/n)	No
Builds Without Errors (y/n)	Y
Unit Tests Pass (y/n)	NA
Documentation Included (y/n)	N

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Change Description

On systems using display scaling, scrollTop may give you a decimal value.

Reference MDN scrollTop

To resolve the scroll issue added 2.0 px tolerance.

Rationale

Since some browsers return sub-pixel values cannot use exact integer number to detect the location of scroll bar.

Testing/Review Recommendations

Manually verified the fix on both Mac and Pc on Chrome 92.0.4515.131 and FireFox 91.0

Future Work

NA