Fix saved hashtags not getting persisted

Pachyderm/Sources/Pachyderm/Model/Hashtag.swift

@@ -34,6 +34,13 @@ public class Hashtag: Codable {
         self.history = try container.decodeIfPresent([History].self, forKey: .history)
     }
     
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        try container.encode(name, forKey: .name)
+        try container.encode(url.absoluteString, forKey: .url)
+        try container.encodeIfPresent(history, forKey: .history)
+    }
+    
     private enum CodingKeys: String, CodingKey {
         case name
         case url