Fix SignedPreKeyRecord NSSecureCoding conformance

Author: max-signal

SignalServiceKit/Storage/AxolotlStore/Model/PreKeyRecord.swift

@@ -9,7 +9,7 @@ private let kCoderCreatedAt = "kCoderCreatedAt"
 
 @objc(PreKeyRecord)
 public class PreKeyRecord: NSObject, NSSecureCoding {
-    public static let supportsSecureCoding: Bool = true
+    public class var supportsSecureCoding: Bool { true }
 
     public let id: Int32
     public let keyPair: ECKeyPair

SignalServiceKit/Storage/AxolotlStore/Model/SignedPreKeyRecord.swift

@@ -10,6 +10,8 @@ private let kCoderPreKeySignature = "kCoderPreKeySignature"
 
 @objc(SignedPreKeyRecord)
 public class SignedPreKeyRecord: PreKeyRecord {
+    public class override var supportsSecureCoding: Bool { true }
+
     public let signature: Data
     public let generatedAt: Date