Fixed array of strings options with custom label and value keys

Fixed array of strings options when using custom value and label keys not rendering correctly.
Changed label and value keys to be set dynamically.

src/virtual-select.js

@@ -1152,7 +1152,7 @@ export class VirtualSelect {
     const prepareOption = (d) => {
       if (typeof d !== 'object') {
         // eslint-disable-next-line no-param-reassign
-        d = { value: d, label: d };
+        d = { [valueKey]: d, [labelKey]: d };
       }
 
       const value = secureText(getString(d[valueKey]));