renamed getLock by readLock to better understanding

Sources/KeychainSwift.swift

@@ -33,7 +33,7 @@ open class KeychainSwift {
   */
   open var synchronizable: Bool = false
 
-  private let getLock = NSLock()
+  private let readLock = NSLock()
   
   /// Instantiate a KeychainSwift object
   public init() { }
@@ -157,8 +157,8 @@ open class KeychainSwift {
   
   */
   open func getData(_ key: String) -> Data? {
-    getLock.lock()
-    defer { getLock.unlock() }
+    readLock.lock()
+    defer { readLock.unlock() }
     let prefixedKey = keyWithPrefix(key)
     
     var query: [String: Any] = [