niv motoko-base: update 520ccf5d -> 712d0587 (#4409)

## Changelog for motoko-base:
Branch: next-moc
Commits: [dfinity/motoko-base@520ccf5d...712d0587](dfinity/motoko-base@520ccf5...712d058)

* [`cba05e81`](dfinity/motoko-base@cba05e8) Publish on Mops ([dfinity/motoko-base⁠#618](https://togithub.com/dfinity/motoko-base/issues/618))
* [`d81f5527`](dfinity/motoko-base@d81f552) Add commit hash to `matchers` dependency ([dfinity/motoko-base⁠#621](https://togithub.com/dfinity/motoko-base/issues/621))
* [`c86d76ff`](dfinity/motoko-base@c86d76f) doc: update `List.mo` ([dfinity/motoko-base⁠#616](https://togithub.com/dfinity/motoko-base/issues/616))
* [`4c2a90e7`](dfinity/motoko-base@4c2a90e) Fix compiler warning in `Array.take()` method ([dfinity/motoko-base⁠#611](https://togithub.com/dfinity/motoko-base/issues/611))

nix/sources.json

@@ -75,10 +75,10 @@
         "homepage": null,
         "owner": "dfinity",
         "repo": "motoko-base",
-        "rev": "520ccf5de395a3a7b408e9c57b8b1e1fc65f04cf",
-        "sha256": "0gbhbsk0rcy7462l8412gf54n0w7ldxw4fsw96wx1hbm65wa06cl",
+        "rev": "712d0587b0c8d2958adf450bd2e1554f2b0ff258",
+        "sha256": "17ghrfgzwlz7hbapy4sq9wbckxqy4xmcj8jpqv68bng9s83zvvvn",
         "type": "tarball",
-        "url": "https://github.com/dfinity/motoko-base/archive/520ccf5de395a3a7b408e9c57b8b1e1fc65f04cf.tar.gz",
+        "url": "https://github.com/dfinity/motoko-base/archive/712d0587b0c8d2958adf450bd2e1554f2b0ff258.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "motoko-matchers": {