Get rid of the _11ty folder—we don’t need it.

.eleventy.js

@@ -33,7 +33,34 @@ module.exports = function(eleventyConfig) {
     return array.slice(0, n);
   });
 
-  eleventyConfig.addCollection("tagList", require("./_11ty/getTagList"));
+  eleventyConfig.addCollection("tagList", function(collection) {
+    let tagSet = new Set();
+    collection.getAll().forEach(function(item) {
+      if( "tags" in item.data ) {
+        let tags = item.data.tags;
+
+        tags = tags.filter(function(item) {
+          switch(item) {
+            // this list should match the `filter` list in tags.njk
+            case "all":
+            case "nav":
+            case "post":
+            case "posts":
+              return false;
+          }
+
+          return true;
+        });
+
+        for (const tag of tags) {
+          tagSet.add(tag);
+        }
+      }
+    });
+
+    // returning an array in addCollection works in Eleventy 0.5.3
+    return [...tagSet];
+  });
 
   eleventyConfig.addPassthroughCopy("img");
   eleventyConfig.addPassthroughCopy("css");