added topics in bracket-push, simple-cipher, crpto-square and atbash-cipher (#910)

* added topics in bracket-push, simple-cipher, crpto-square and atbash-cipher

* added topics in bracket-push, simple-cipher, crpto-square and atbash-cipher

config.json

       "core": false,
       "difficulty": 5,
       "slug": "bracket-push",
-      "topics": null,
+      "topics": [
+        "stacks",
+        "strings"
+      ],
       "unlocked_by": "flatten-array",
       "uuid": "85aa50ac-0141-49eb-bc6f-62f3f7a97647"
     },
       "core": false,
       "difficulty": 5,
       "slug": "atbash-cipher",
-      "topics": null,
+      "topics": [
+        "strings",
+        "cryptography",
+        "security"
+      ],
       "unlocked_by": "rotational-cipher",
       "uuid": "d36ce010-210f-4e9a-9d6c-cb933e0a59af"
     },
       "core": false,
       "difficulty": 7,
       "slug": "crypto-square",
-      "topics": null,
+      "topics": [
+        "strings",
+        "text_formatting",
+        "mathematics",
+        "cryptography",
+        "security",
+        "lists"
+      ],
       "unlocked_by": "rotational-cipher",
       "uuid": "162bebdc-9bf2-43c0-8460-a91f5fc16147"
     },
       "core": false,
       "difficulty": 8,
       "slug": "simple-cipher",
-      "topics": null,
+      "topics": [
+        "strings",
+        "cryptography",
+        "security",
+        "mathematics",
+        "randomness",
+        "exception_handling"
+      ],
       "unlocked_by": "rotational-cipher",
       "uuid": "f654831f-c34b-44f5-9dd5-054efbb486f2"
     },