[Minor] Fix icons in doc (#165)

Author: WoosukKwon

docs/source/index.rst

@@ -15,9 +15,10 @@ Welcome to vLLM!
    </p>
 
    <p style="text-align:center">
-   <a class="github-button" href="https://github.com/vllm-project/vllm" data-show-count="true" data-size="large" aria-label="Star skypilot-org/skypilot on GitHub">Star</a>
-   <a class="github-button" href="https://github.com/vllm-project/vllm/subscription" data-icon="octicon-eye" data-size="large" aria-label="Watch skypilot-org/skypilot on GitHub">Watch</a>
-   <a class="github-button" href="https://github.com/vllm-project/vllm/fork" data-icon="octicon-repo-forked" data-size="large" aria-label="Fork skypilot-org/skypilot on GitHub">Fork</a>
+   <script async defer src="https://buttons.github.io/buttons.js"></script>
+   <a class="github-button" href="https://github.com/vllm-project/vllm" data-show-count="true" data-size="large" aria-label="Star">Star</a>
+   <a class="github-button" href="https://github.com/vllm-project/vllm/subscription" data-icon="octicon-eye" data-size="large" aria-label="Watch">Watch</a>
+   <a class="github-button" href="https://github.com/vllm-project/vllm/fork" data-icon="octicon-repo-forked" data-size="large" aria-label="Fork">Fork</a>
    </p>