:bug: invalid var assignment fix

vue-theme/src/pages/single.vue

          */
         checkAndSetHero(post) {
             if(!post) return
-            const json = { url: post.featured, heroType: 'image' }
+            let json = { url: post.featured, heroType: 'image' }
             if(post.hero && JSON.parse(post.hero).url) {
                 json = JSON.parse(post.hero)
                 json.heroType = 'video'