niv motoko-base: update a8e12e0f -> 9927b43f (#3323)

## Changelog for motoko-base:
Branch: next-moc
Commits: [dfinity/motoko-base@a8e12e0f...9927b43f](dfinity/motoko-base@a8e12e0...9927b43)

* [`7ca5b2c8`](dfinity/motoko-base@7ca5b2c) Clean up: Array to buffer as `Buffer.fromArray`, (not `Array.buffer`). ([dfinity/motoko-base⁠#389](https://togithub.com/dfinity/motoko-base/issues/389))

nix/sources.json

@@ -64,10 +64,10 @@
         "homepage": null,
         "owner": "dfinity",
         "repo": "motoko-base",
-        "rev": "a8e12e0f44c710552c2b03b8a4a2f57afaf27f78",
-        "sha256": "1pl26vwh3i5pi90vbi4x4sh2b297d4jdnardd2ihqlg5zmxrhwxj",
+        "rev": "9927b43fdf3feaf8272e023b639cbb80a0197487",
+        "sha256": "1pnch81lwcs0xfsih1gmzdkqackj97y3mz1cmrd0a2csinvxkmlx",
         "type": "tarball",
-        "url": "https://github.com/dfinity/motoko-base/archive/a8e12e0f44c710552c2b03b8a4a2f57afaf27f78.tar.gz",
+        "url": "https://github.com/dfinity/motoko-base/archive/9927b43fdf3feaf8272e023b639cbb80a0197487.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "motoko-matchers": {