Select component requires `customValue` prop

[edrpls]

According to the documentation, the customValue prop on the Select component should be optional and used only for customization. However, it is required to set it, or React will complain about elements in an array without a key prop.

The component needs something like:

const valueKey = customValue || 'value';
/* ... */
 <option key={o[valueKey]} value={o[valueKey]}>

[edrpls]

This is fixed on feature/improved-gumdrops, possibly to be released as 2.0.0 in the future.