Add justifyContent: 'space-evenly' to Flexbox.propTypes

[pcatkins]

Hi all, thanks for the great project!

nitpick: Suggesting to add 'space-evenly' as acceptable value for justifyContent prop:

 justifyContent: PropTypes.oneOf([
    'center',
    'flex-end',
    'flex-start',
    'space-around',
    'space-between'
  ]),

[dumboluzz]

I ran into the same problem just now.

I'm gonna make a quick PR #53.

[kouak]

Likewise, other possible values are missing. See here : https://developer.mozilla.org/fr/docs/Web/CSS/justify-content

Missing values :

• stretch
• left
• right
• start
• end
• normal
• safe
• unsafe