Update README.md

Author: spacejam

README.md

@@ -9,7 +9,7 @@
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         <td><a href="https://github.com/sponsors/spacejam">buy a coffee for us to convert into databases</a></td>
-        <td><a href="https://github.com/sponsors/spacejam"><img src="https://img.shields.io/opencollective/backers/sled"></a></td>
+        <td><a href="https://github.com/sponsors/spacejam"><img src="https://img.shields.io/github/sponsors/spacejam"></a></td>
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         <td><a href="https://docs.rs/sled">documentation</a></td>