Update _adjustments.html.erb

This fixes the fact that a promotion may display twice.
Zipcode and Phone required depending on the model

Backport of part of the commit https://github.com/200Creative/spree_bootstrap_frontend/commit/2b74b23b9113246def85fffd5e978cf8e280e041
those lines are also relevant for this branch
(checked in https://github.com/spree/spree/blob/2-3-stable/frontend/app/views/spree/address/_form.html.erb)
Merge pull request #88 from fsainz/patch-1

Zipcode and Phone required depending on the model
Merge pull request #87 from tesserakt/patch-1

Update _adjustments.html.erb
#90
Merge pull request #92 from alain-andre/2-3-stable

Fix #90.

Ports a fix from Spree that is not present in our 2-3-stable branch.