Add stringToDate filter

because the RSS plugin's date filters will only take an actual date

.eleventy.js

@@ -15,6 +15,8 @@ module.exports = function (eleventyConfig) {
     "node_modules/simpledotcss/simple.css": "css/simple.css",
   });
 
+  eleventyConfig.addFilter("stringToDate", function (value) {
+    return new Date(value);
   });
   eleventyConfig.addFilter("formatDatetimeForHumans", function (value) {
     const dt = new Date(value);