message: fix readme, Option actually allows number type
diff: @@ -131,8 +131,8 @@ React.render(c, container);
  |----------|----------------|----------|--------------|
  |className | additional class to option | String | '' |
  |disabled | no effect for click or keydown for this item | bool | false |
  -|key | if react want you to set key, then key is same as value, you can omit value | String | - |
  -|value | default filter by this attribute. if react want you to set key, then key is same as value, you can omit value | String | - |
  +|key | if react want you to set key, then key is same as value, you can omit value | String/number | - |
  +|value | default filter by this attribute. if react want you to set key, then key is same as value, you can omit value | String/number | - |
  |title | if you are not satisfied with auto-generated `title` which is show while hovering on selected value, you can customize it with this property | String | - |
  