[stats][boxplot] fix container props calculation

[williaster]

🐛 Bug Fix

• fixes the container calculation for <Boxplot /> in @vx/stats (it appeared broken for horizontal and vertical positions, rendering negative widths etc)
• moves outliers to the bottom-most layer of the <Boxplot />

This is the container element (styled) afterward, for both orientations

🚀 Enhancements

• adds class names to the outlier circles and boxplot box rect

cc @conglei

[conglei]

Thanking for catching this issue! and fix look good!

[williaster]

Hmm builds seem to be stuck:

lerna info Installing external dependencies

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received```

[hshoff]

LGTM