fix(core): do not force using FormGroup when FieldArray is set. (#894)
fix(core): do not force using FormGroup when FieldArray is set. (#894)

fix #890
formly-js/ng-formly,ngx-formly/ngx-formly,formly-js/ng-formly,formly-js/ng2-formly,ngx-formly/ngx-formly,formly-js/ng2-formly,ngx-formly/ngx-formly,formly-js/ng2-formly,ngx-formly/ngx-formly