Update latest.txt for 2.16.1 and 2.15.4

scripts/latest.txt

@@ -1,10 +1,10 @@
 {
-    "version": "2.16",
+    "version": "2.16.1",
     "url":     "https://docs.wagtail.org/en/stable/releases/2.16.html",
-    "minorUrl": "https://docs.wagtail.org/en/stable/releases/2.16.html",
+    "minorUrl": "https://docs.wagtail.org/en/stable/releases/2.16.1.html",
     "lts": {
-        "version": "2.15.3",
-        "url": "https://docs.wagtail.org/en/stable/releases/2.15.3.html",
+        "version": "2.15.4",
+        "url": "https://docs.wagtail.org/en/stable/releases/2.15.4.html",
         "minorUrl": "https://docs.wagtail.org/en/stable/releases/2.15.html"
     }
 }