Fix LidarScan properties.

Sources/SwiftRPLidar/SwiftRPLidar.swift

@@ -46,10 +46,10 @@ func processScan(raw: Data) throws -> LidarScan {
 }
 
 public struct LidarScan{
-    var newScan: Bool
-    var quality: UInt8
-    var angle: Float
-    var distance: Float
+    public let newScan: Bool
+    public let quality: UInt8
+    public let angle: Float
+    public let distance: Float
 }