niv candid: update 171a58dd -> 6313d973 (#4750)

## Changelog for candid:
Branch: master
Commits: [dfinity/candid@171a58dd...6313d973](dfinity/candid@171a58d...6313d97)

* [`6313d973`](dfinity/candid@6313d97) bump ic-agent ([dfinity/candid⁠#580](https://github.com/dfinity/candid/issues/580))

nix/sources.json

@@ -6,10 +6,10 @@
         "homepage": "",
         "owner": "dfinity",
         "repo": "candid",
-        "rev": "171a58dde0a672d59bc6f875069cae87c4270dce",
-        "sha256": "0l7cy0pvsw2mnyway22m8y4c0d7liackbkggs03vrjrj50b9fpw4",
+        "rev": "6313d9732f7538aa7b7ccdb4ff0cb7d4e2cc4206",
+        "sha256": "026xzddqrkk6076sxqv189zxjg4fv462ax5kq6gq38df5g35y441",
         "type": "tarball",
-        "url": "https://github.com/dfinity/candid/archive/171a58dde0a672d59bc6f875069cae87c4270dce.tar.gz",
+        "url": "https://github.com/dfinity/candid/archive/6313d9732f7538aa7b7ccdb4ff0cb7d4e2cc4206.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "esm": {