fix difficulties (#16)

Author: quintuple-mallard

config.json

@@ -68,15 +68,15 @@
         "uuid": "b5f2fe48-d2cc-4843-bc51-e6c76af46f91",
         "practices": [],
         "prerequisites": [],
-        "difficulty": 1
+        "difficulty": 2
       },
       {
         "slug": "resistor-color-duo",
         "name": "Resistor Color Duo",
         "uuid": "e4c59681-3664-4ad4-8948-83b6084ad244",
         "practices": [],
         "prerequisites": [],
-        "difficulty": 1
+        "difficulty": 2
       },
       {
         "slug": "resistor-color",
@@ -92,7 +92,7 @@
         "uuid": "a1f5a88f-aa72-405f-88a3-e1a120ce3a89",
         "practices": [],
         "prerequisites": [],
-        "difficulty": 1
+        "difficulty": 4
       },
       {
         "slug": "grep",
@@ -138,4 +138,4 @@
     "typing/static",
     "used_for/scripts"
   ]
-}
+}