Remove versionDate from the stats display

data/2025-03-04-stats.json

 {
-  "versionDate": "",
   "antibodies": 1355665,
   "species": [
     "Homo sapiens",

src/server/models/Statistics.js

@@ -36,6 +36,9 @@ export class Statistics {
    */
   toString() {
     return JSON.stringify(this, (key, value) => {
+      // Don't include versionDate
+      if (key === 'versionDate') return undefined
+
       return value instanceof Set ? [...value] : value
     }, 2)
   }