Add more test about SDAnimatedImage

Tests/Tests/SDAnimatedImageTest.m

@@ -218,6 +218,7 @@ static const NSUInteger kTestGIFFrameCount = 5; // local TestImage.gif loop coun
             // Progressive image may be nil when download data is not enough
             if (image) {
                 expect(image.sd_isIncremental).beTruthy();
+                expect([image conformsToProtocol:@protocol(SDAnimatedImage)]).beTruthy();
                 BOOL isProgressive = imageView.isProgressive;
                 expect(isProgressive).equal(YES);
             }