switch back to sorting by date

this works again, possibly due to the better archiving. And as epoch
sometimes makes a bad 'find first year' result, it's better to use this.
diff --git a/site/api/stats.lua b/site/api/stats.lua
index 077d1e2..f91d9b7 100644
--- a/site/api/stats.lua
+++ b/site/api/stats.lua
@@ -380,7 +380,7 @@
             
             sort = {
                 {
-                    epoch = {
+                    date = {
                         order = "asc"
                     }
                 }