Do not let Xcode compressed APNG files.

Demo/YYTextDemo.xcodeproj/project.pbxproj

@@ -698,6 +698,7 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = com.ibireme.YYTextDemo;
 				PRODUCT_NAME = "$(TARGET_NAME)";
+				STRIP_PNG_TEXT = NO;
 			};
 			name = Debug;
 		};
@@ -711,6 +712,7 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = com.ibireme.YYTextDemo;
 				PRODUCT_NAME = "$(TARGET_NAME)";
+				STRIP_PNG_TEXT = NO;
 			};
 			name = Release;
 		};