Quick fix to handle http keys

This fixes the case in which keys are not simple strings, but urls such as "http://purl.org/dc/terms/created", the keys are no longer split by '.' in this case, thus breaking object functionality. For example:

considering

_source1 = {
  author: {
    first: 'John',
    last: 'Doe'
  }
}

_source2 = {
  "http://purl.org/dc/terms/creator": {
    first: 'John',
    last: 'Doe'
  }
}


"author.first" works but "http://purl.org/dc/terms/creator.last" will not work