ocr-numbers: estimate difficulty and position

config.json

       "topics": []
     },
     {
-      "slug": "rectangles",
-      "difficulty": 7,
-      "topics": []
-    },
-    {
       "slug": "meetup",
       "difficulty": 7,
       "topics": []
       "topics": []
     },
     {
+      "slug": "ocr-numbers",
+      "difficulty": 8,
+      "topics": []
+    },
+    {
+      "slug": "rectangles",
+      "difficulty": 8,
+      "topics": []
+    },
+    {
       "slug": "book-store",
       "difficulty": 8,
       "topics": []
       "topics": []
     },
     {
-      "slug": "ocr-numbers",
-      "difficulty": 1,
-      "topics": []
-    },
-    {
       "slug": "run-length-encoding",
       "difficulty": 1,
       "topics": []