Problem:
Numeric values are suffixed with 'px', unless the property supports
unitless values. However, vendor prefixed properties were ignored
resulting in invalid CSS values for properties like
'-webkit-flex-shrink'.
Solution:
Apply the upstream solution from React, which includes vendor prefixed
properties in the "unitless number" map. Also build a custom vendor
prefixer to ensure adequate browser support (i.e., Safari 7 and older
Chrome).
