message: replace Box+position w/Absolute in MergeButton demo
diff: import React from 'react'
  import PropTypes from 'prop-types'
  -import {Box, Button, PointerBox, Details, Text} from '../../src'
  +import {Absolute, Box, Button, Caret, PointerBox, Details, Text} from '../../src'
  const MergeButton = ({numCommits, onClick, primary}) => {
  const arrowStyles = {
  @@ -36,7 +36,7 @@ const MergeButton = ({numCommits, onClick, primary}) => {
  <Button is="summary" {...buttonSchemeProps} onClick={toggle} style={borderStyles}>
  <div className="d-inline-block v-align-middle" style={arrowStyles} />
  </Button>
  - <Box position="absolute" width={300} mt={1} style={{zIndex: 99999}}>
  + <Absolute mt={1} width={300} zIndex={99999} boxShadow="small">
  <PointerBox caret="top-left">
  <ul className="list-style-none p-0 m-0">
  <li className="border-bottom py-2 pl-4 pr-2">
  @@ -65,7 +65,7 @@ const MergeButton = ({numCommits, onClick, primary}) => {
  </li>
  </ul>
  </PointerBox>
  - </Box>
  + </Absolute>
  </React.Fragment>
  )}
  </Details>
  