skeleton: "Bhm" is not supported

I used skeleton: "Bhm" to format a date.
It throwed following exception:
  code: 'E_INVALID_OPTIONS',
  invalidField: 'B',
  type: 'skeleton',
  value: 'Bhm'

My code:
```
var format2 = Globalize("zh-Hans").dateFormatter({ skeleton: "Bhm"})(new Date());
console.log(format2);
```
Could you please support 'B' in skeleton?