fix(theme): always add alt attribute to images (#1348)

src/client/theme-default/components/VPImage.vue

@@ -20,6 +20,7 @@ export default {
       class="VPImage"
       v-bind="typeof image === 'string' ? $attrs : { ...image, ...$attrs }"
       :src="withBase(typeof image === 'string' ? image : image.src)"
+      :alt="typeof image === 'string' ? '' : (image.alt || '')"
     />
     <template v-else>
       <VPImage class="dark" :image="image.dark" v-bind="$attrs" />