add 'pubDate' for RSS feeds

inc/teddit_api/handleSubreddit.js

@@ -69,6 +69,7 @@ module.exports = function() {
             <title>${link.title}</title>
             <author>${link.author}</author>
             <created>${link.created}</created>
+            <pubDate>${new Date(link.created_utc*1000).toGMTString()}</pubDate>
             <domain>${link.domain}</domain>
             <id>${link.id}</id>
             <thumbnail>${thumbnail}</thumbnail>

inc/teddit_api/handleUser.js

@@ -74,6 +74,7 @@ module.exports = function() {
             <kind>${kind}</kind>
             <subreddit>${post.subreddit}</subreddit>
             <created>${post.created_utc}</created>
+            <pubDate>${new Date(post.created_utc*1000).toGMTString()}</pubDate>
             <ups>${post.ups}</ups>
             <link>${permalink}</link>
             <edited>${post.edited}</edited>