Fix PoW calculation

SignalServiceKit/src/Loki/API/LokiAPI+Message.swift

@@ -40,7 +40,8 @@ public extension LokiAPI {
                         if isPoWRequired {
                             // The storage server takes a time interval in milliseconds
                             let now = NSDate.ows_millisecondTimeStamp()
-                            if let nonce = ProofOfWork.calculate(data: data, pubKey: destination, timestamp: now, ttl: ttl) {
+                            let ttlInSeconds = ttl / 1000
+                            if let nonce = ProofOfWork.calculate(data: data, pubKey: destination, timestamp: now, ttl: ttlInSeconds) {
                                 let result = Message(destination: destination, data: data, ttl: ttl, timestamp: now, nonce: nonce)
                                 seal.fulfill(result)
                             } else {

SignalServiceKit/src/Loki/Crypto/ProofOfWork.swift

@@ -63,7 +63,7 @@ public enum ProofOfWork {
     ///   - data: The message data
     ///   - pubKey: The message recipient
     ///   - timestamp: The timestamp
-    ///   - ttl: The message time to live
+    ///   - ttl: The message time to live, in **seconds**
     /// - Returns: A nonce string or `nil` if it failed
     public static func calculate(data: String, pubKey: String, timestamp: UInt64, ttl: UInt64) -> String? {
         let payload = createPayload(pubKey: pubKey, data: data, timestamp: timestamp, ttl: ttl)