Update PusherConnection.swift

Author: dmorrow

Sources/PusherConnection.swift

@@ -176,6 +176,15 @@ public typealias PusherEventJSON = [String: AnyObject]
             self.channels.remove(name: channelName)
         }
     }
+    
+    /**
+        Unsubscribes from all PusherChannels
+    */
+    internal func unsubscribeAll() {
+        for (_, channel) in channels.channels {
+            pusher.unsubscribe(channel.name)
+        }
+    }
 
     /**
         Either writes a string directly to the websocket with the given event name