niv motoko-base: update 5400497c -> 5aa550ed (#4504)

## Changelog for motoko-base:
Branch: next-moc
Commits: [dfinity/motoko-base@5400497c...5aa550ed](dfinity/motoko-base@5400497...5aa550e)

* [`b0c4904d`](dfinity/motoko-base@b0c4904) doc: update `Float.mo` documentation ([dfinity/motoko-base⁠#631](https://togithub.com/dfinity/motoko-base/issues/631))
* [`281f8bd3`](dfinity/motoko-base@281f8bd) doc: update `Region.mo` ([dfinity/motoko-base⁠#632](https://togithub.com/dfinity/motoko-base/issues/632))

nix/sources.json

@@ -75,10 +75,10 @@
         "homepage": null,
         "owner": "dfinity",
         "repo": "motoko-base",
-        "rev": "5400497cb002fe57e33502a7f0240fb75c0c98b6",
-        "sha256": "0i1iws9zj04lacvl6dd9kzxxsp2bcbva9vv3gg12xw1byg61j2hi",
+        "rev": "5aa550edc5814fb02cf9d5e9c22a62cbdda764c5",
+        "sha256": "03i9pdgyzqicv7cdzrlzbr2qkl0n51gp76fz4hg9n4bb6w2z7zzr",
         "type": "tarball",
-        "url": "https://github.com/dfinity/motoko-base/archive/5400497cb002fe57e33502a7f0240fb75c0c98b6.tar.gz",
+        "url": "https://github.com/dfinity/motoko-base/archive/5aa550edc5814fb02cf9d5e9c22a62cbdda764c5.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "motoko-matchers": {