Override field twig template in views
It needs to be:

views-view-field--[field-machine-name].html.twig

If you look in Manage Fields, your field machine name is probably field_this_is_field. 

Therefore, in your case:

views-view-field--field-this-is-field.html

Note that this is will override for all views that have this field, if you want to only target a specific view use:

views-view-field--[view-machine-name]--[field-machine-name].html.twig