fix: align on "verificationMethod" as mandated by did-core

specifications/credential.issuance.protocol.md

@@ -247,13 +247,13 @@ The following is a non-normative example of a `CredentialStatus` response object
 create [=Verifiable Credential] proofs. Key rotation and revocation may be supported in the following way:
 
 1. After a defined `cryptoperiod`, a rotation is initiated, a new key pair is generated and the public key is added
-   to a `verficationMethod` in the [=Credential Issuer=] DID document. The new private key is used to sign newly
+   to a `verificationMethod` in the [=Credential Issuer=] DID document. The new private key is used to sign newly
    issued [=Verifiable Credential=] proofs.
-2. The old private key is decommissioned (archived or destroyed). However, `verificationMethods` in
+2. The old private key is decommissioned (archived or destroyed). However, `verificationMethod` in
    the [=Credential Issuer=] DID document are retained so existing issued [=Verifiable Credentials=] may be verified.
 3. At some point before existing [=Verifiable Credentials=] are set to expire, an [=Credential Issuer=] may make
    credential offers for new [=Verifiable Credentials=] to [=Holders=].
-4. After a defined period, revocation will be performed where the public key's `verificationMethods` will be removed
+4. After a defined period, revocation will be performed where the public key's `verificationMethod` will be removed
    from the [=Credential Issuer=] DID document. At this point, any existing [=Verifiable Credentials=] with proofs
    signed by the revoked key will not verify.