Update index.md

"chains chains" --> chains

Author: zkpub

docs/cdk/index.md

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    <div class="hero-image"><img src="../img/cdk/cdk.svg" loading="lazy" class="hero-image" style="width: 40%; float: right;"></div>
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       <h1 class="hero-heading">Polygon CDK</h1>
-      <p class="hero-subtext">Polygon Chain Development Kit (CDK) is a modular, open source software toolkit allowing blockchain developers to launch new zero-knowledge proof (zkEVM plus optional validium) L2 chains chains on Ethereum.</p>
+      <p class="hero-subtext">Polygon Chain Development Kit (CDK) is a modular, open source software toolkit allowing blockchain developers to launch new zero-knowledge proof (zkEVM plus optional validium) L2 chains on Ethereum.</p>
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