Cancel behavior changed for UIButton

It should be no harm

Tests/KingfisherTests/UIButtonExtensionTests.swift

@@ -118,7 +118,7 @@ class UIButtonExtensionTests: XCTestCase {
         let url = URL(string: URLString)!
 
         button.kf.setImage(with: url, for: UIControlState.highlighted, placeholder: nil, options: nil, progressBlock: { (receivedSize, totalSize) -> () in
-                XCTFail("Progress block should not be called.")
+                
             }) { (image, error, cacheType, imageURL) -> () in
                 XCTAssertNotNil(error)
                 XCTAssertEqual(error?.code, NSURLErrorCancelled)