Add protocol for serial library to implement.

Sources/SwiftRPLidar/SwiftRPLidar.swift

@@ -1,5 +1,5 @@
 import Foundation
-import SwiftSerial
+import LidarSerial
 
 struct Constants{
     static let SYNC: UInt8 = 0xA5
@@ -64,11 +64,11 @@ typealias ScanHandler = (_ scans: [LidarScan]) -> Void
 
 class RPLidar{
     private var motor: Bool = false
-    private var serialPort: SerialPort? = nil
+    private var serialPort: LidarSerial? = nil
     private var motorRunning = false
     
     
-    init(serialPort: SerialPort) throws {
+    init(serialPort: LidarSerial) throws {
         self.serialPort = serialPort
 
     }