Update design_config_form.xml

Missing apng extension in 'allowedExtensions' parameter

Author: WaPoNe

app/code/Magento/Theme/view/adminhtml/ui_component/design_config_form.xml

@@ -67,7 +67,7 @@
                         <item name="componentType" xsi:type="string">fileUploader</item>
                         <item name="notice" xsi:type="string" translate="true">Allowed file types: ico, png, gif, jpg, jpeg, apng, svg. Not all browsers support all these formats!</item>
                         <item name="maxFileSize" xsi:type="number">2097152</item>
-                        <item name="allowedExtensions" xsi:type="string">jpg jpeg gif png svg ico</item>
+                        <item name="allowedExtensions" xsi:type="string">jpg jpeg gif png svg ico apng</item>
                         <item name="uploaderConfig" xsi:type="array">
                             <item name="url" xsi:type="string">theme/design_config_fileUploader/save</item>
                         </item>