Update docs

docs/DataSources.html

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         <a class="header-link" href="index.html">
           DiffableDataSources Docs
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-         (96% documented)
+         (98% documented)
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-      <p>&copy; 2020 <a class="link" href="https://github.com/ra1028" target="_blank" rel="external">Ryo Aoyama</a>. All rights reserved. (Last updated: 2020-04-12)</p>
+      <p>&copy; 2021 <a class="link" href="https://github.com/ra1028" target="_blank" rel="external">Ryo Aoyama</a>. All rights reserved. (Last updated: 2021-06-09)</p>
       <p>Generated by <a class="link" href="https://github.com/realm/jazzy" target="_blank" rel="external">jazzy ♪♫ v0.11.2</a>, a <a class="link" href="https://realm.io" target="_blank" rel="external">Realm</a> project.</p>
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