fix pathPrefix for rss feed (v0.9.17)

gatsby-config.js

@@ -87,11 +87,11 @@ module.exports = {
                         }
                     }
                     site {
+                        pathPrefix
                         siteMetadata {
                             title
                             description
                             siteUrl
-                            pathPrefix
                         }
                     }
                 }
@@ -100,26 +100,20 @@ module.exports = {
                     {
                         serialize: ({ query: { site, directus } }) => {
                             return directus.news.map((item) => {
+                                const baseUrl = [
+                                    site.siteMetadata.siteUrl,
+                                    site.pathPrefix || "",
+                                    "news",
+                                ].join("/")
+
                                 return Object.assign(
                                     {},
                                     {
                                         title: item.title,
                                         description: item.content,
                                         date: item.date_published,
-                                        url:
-                                            site.siteMetadata.siteUrl +
-                                            "/" +
-                                            (site.siteMetadata.pathPrefix ||
-                                                "") +
-                                            "/news/" +
-                                            item.slug,
-                                        guid:
-                                            site.siteMetadata.siteUrl +
-                                            "/" +
-                                            (site.siteMetadata.pathPrefix ||
-                                                "") +
-                                            "/news/" +
-                                            item.slug,
+                                        url: baseUrl + "/" + item.slug,
+                                        guid: baseUrl + "/" + item.slug,
                                         category: "news",
                                     }
                                 )