[snapshot] Replace Objective-C-style NSMakeRange with Swift-style NSR…

…ange.init (#15128)

* Replace Objective-C-style NSMakeRange with Swift-style NSRange.init

Replace Objective-C-style NSMakeRange(0, simulator.count) with Swift-style NSRange(location: 0, length: simulator.count) (suggested by SwiftLint https://github.com/realm/SwiftLint). Delete empty line.

* Increment SnapshotHelperVersion to 1.21

snapshot/lib/assets/SnapshotHelper.swift

@@ -175,11 +175,11 @@ open class Snapshot: NSObject {
 
             let screenshot = XCUIScreen.main.screenshot()
             guard var simulator = ProcessInfo().environment["SIMULATOR_DEVICE_NAME"], let screenshotsDir = screenshotsDirectory else { return }
-            
+
             do {
                 // The simulator name contains "Clone X of " inside the screenshot file when running parallelized UI Tests on concurrent devices
                 let regex = try NSRegularExpression(pattern: "Clone [0-9]+ of ")
-                let range = NSMakeRange(0, simulator.count)
+                let range = NSRange(location: 0, length: simulator.count)
                 simulator = regex.stringByReplacingMatches(in: simulator, range: range, withTemplate: "")
 
                 let path = screenshotsDir.appendingPathComponent("\(simulator)-\(name).png")
@@ -300,4 +300,4 @@ private extension CGFloat {
 
 // Please don't remove the lines below
 // They are used to detect outdated configuration files
-// SnapshotHelperVersion [1.20]
+// SnapshotHelperVersion [1.21]