fix Referencing a DOM node in Expression Error
fix Referencing a DOM node in Expression Error

See [angular document]
(https://docs.angularjs.org/error/$parse/isecdom?p0=editable)
in details. To avoid the error, select editable DOM directly
rather than DOM summernote returned.
close #25

summernote/angular-summernote,uncedric/angular-summernote,thomaslhostis/angular-summernote