Use absolute migration guide URL to dev.y.c

Author: emlun

doc/Migrating_from_v1.adoc

@@ -11,7 +11,7 @@ link:https://github.com/Yubico/java-webauthn-server/issues/new[let us know!]
 
 This is the migration guide for the core library.
 The `webauthn-server-attestation` module has
-link:/java-webauthn-server/webauthn-server-attestation/doc/Migrating_from_v1.adoc[its own migration guide].
+link:https://developers.yubico.com/java-webauthn-server/webauthn-server-attestation/doc/Migrating_from_v1.html[its own migration guide].
 
 Here is a high-level outline of what needs to be updated: