rotational-cipher: move to end of track

config.json

       ]
     },
     {
-      "slug": "rotational-cipher",
-      "difficulty": 1,
-      "topics": [
-
-      ]
-    },
-    {
       "slug": "rna-transcription",
       "difficulty": 2,
       "topics": [
       "topics": [
 
       ]
+    },
+    {
+      "slug": "rotational-cipher",
+      "difficulty": 1,
+      "topics": [
+
+      ]
     }
   ],
   "deprecated": [