Fix macOS demo build issue

Author: dreampiggy

Example/SDWebImageSVGCoder-Example-macOS/ViewController.m

@@ -49,7 +49,7 @@ - (void)viewDidLoad {
                     NSAnimationContext *currentContext = [NSAnimationContext currentContext];
                     currentContext.duration = 2;
                     imageView2.animator.bounds = CGRectMake(0, 0, screenSize.width / 2, screenSize.height);
-                }];
+                } completionHandler:nil];
             }];
         }
     }];