niv motoko-base: update 5811560c -> 1274f8de (#4751)

## Changelog for motoko-base:
Branch: next-moc
Commits: [dfinity/motoko-base@5811560c...1274f8de](dfinity/motoko-base@5811560...1274f8d)

* [`39e12261`](dfinity/motoko-base@39e1226) chore(deps-dev): bump elliptic from 6.5.7 to 6.6.0 ([dfinity/motoko-base⁠#668](https://togithub.com/dfinity/motoko-base/issues/668))
* [`7b5d31e7`](dfinity/motoko-base@7b5d31e) chore(deps-dev): bump secp256k1 from 4.0.3 to 4.0.4 ([dfinity/motoko-base⁠#667](https://togithub.com/dfinity/motoko-base/issues/667))

nix/sources.json

@@ -75,10 +75,10 @@
         "homepage": "",
         "owner": "dfinity",
         "repo": "motoko-base",
-        "rev": "5811560cee7fe82e31baaab7d6d856db85337e1a",
-        "sha256": "1kxsp74x2dcvzihhf6h6xmyvzrl246f7pmiwm8x9pnbrh5pqfb21",
+        "rev": "1274f8deb57f26f88a9802b45a1a24d7c98aad8a",
+        "sha256": "15k597zqkyvml2m89q64iny7gp5x0vxycrbacm6n0xxx2bp8lgsm",
         "type": "tarball",
-        "url": "https://github.com/dfinity/motoko-base/archive/5811560cee7fe82e31baaab7d6d856db85337e1a.tar.gz",
+        "url": "https://github.com/dfinity/motoko-base/archive/1274f8deb57f26f88a9802b45a1a24d7c98aad8a.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "motoko-matchers": {