Change needs to be added to FormlyTemplateOptions

[jrgleason]

I'm submitting a ... (check one with "x")

[X] bug report
[ ] feature request
[ ] support request

Current behavior
The code is as follows...

export interface FormlyFieldConfig {
   ...
   change?: Function;
   ...
}

however, per http://plnkr.co/edit/OfcprFL35FxG3cHpF0Hz?p=preview, if I try to use this property it doesn't work like this this.connectorFields[0].change. I instead need to add it to the FormlyTemplateOptions like this... this.connectorFields[0].templateOptions.change.

Now in plunker this works OK but if you are transpiling with something like webpack you get...

(27,49): error TS2339: Property 'change' does not exist on type 'FormlyTemplateOptions'

so I instead have to use this.connectorFields[0].templateOptions["change"]

Expected behavior
I would like to be able to use this.connectorFields[0].templateOptions.change instead

Minimal reproduction of the problem with instructions

See plunker