message: change tag to is in Sandbox
diff: @@ -9,7 +9,7 @@ Object.assign(components, {NavLink})
  const code = `
  <Block p={4}>
  <Heading>Hello World!</Heading>
  - <Text tag='p'>
  + <Text is='p'>
  All of the primer-react <NavLink to='/components'>components</NavLink> are available in this sandbox!
  </Text>
  <Box my={4} p={2}>
  