datetime validation errors return wrong type name

[jstoiko]

given the type:

date: {
  type: 'datetime'
}

and the value:

date: 'Sun, 28 Feb 2016 16:41:41 GMT'

error.getSource().facetName() returns should be datetime-only. I would expect it to return should be datetime

same thing goes with:

date: {
  type: 'datetime',
  format: 'rfc2616'
}

and the value:

date: '2016-02-28T16:41:41.090Z'