fix twitter and github post links

lib/mdx.js

@@ -76,6 +76,7 @@ export async function getFileBySlug(type, slug) {
       wordCount: content.split(/\s+/gu).length,
       readingTime: readingTime(content),
       slug: slug || null,
+      fileName: fs.existsSync(mdxPath) ? `${slug}.mdx` : `${slug}.md`,
       ...data,
     },
   }
@@ -87,7 +88,6 @@ export async function getAllFilesFrontMatter(type) {
   const allFrontMatter = files.reduce((allPosts, postSlug) => {
     const source = fs.readFileSync(path.join(root, 'data', type, postSlug), 'utf8')
     const { data } = matter(source)
-
     return [
       {
         ...data,