fix: fix threshold option not applying snap threshold

[malangfox]

Issue

#844

Details

• When determining the snapThreshold in _calcSnapThreshold, the value of the threshold option for the Flicking instance must be applied.
• We didn't have a unit test that used vertical Flicking (DEFAULT_VERTICAL in a unit test) and this is the first time we've used it, I fixed it to be similar to the Flicking for other tests.

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[coveralls]

coverage: 82.661% (+0.02%) from 82.638%
when pulling 39b1edd on malangfox:fix-vertical-threshold
into 3d52804 on naver:master.

[daybrush]

LGTM