:x-frame-options DENY is not a valid value

[SevereOverfl0w]

This causes warnings on the host page console.

The following lines probably should check that :x-frame-options value is
truthy (and default to true) instead. The docs should also be updated
accordingly.

yada/src/yada/security.clj

Lines 366 to 367 in c6cb858

	true (assoc-in [:response :headers "x-frame-options"]
	(get-in ctx [:resource :x-frame-options] "SAMEORIGIN"))