index.html: fix issues with software license links (#3221)

* Fix broken copy license links
* Fix reversed GPL and LGPL links

index.html

@@ -36,8 +36,8 @@ backing layer.
 
 <p>
 Ethereum may also be run in a private environment, such as for use within a corporate network,
-without any cost. All core source is licensed under the <a href="https://github.com/ethereum/go-ethereum/tree/master/COPYING.md">LGPL</a>
-and all frontend code is licensed under <a href="https://github.com/ethereum/go-ethereum/tree/master/COPYING.LESSER.md">GPL</a>.
+without any cost. All core source is licensed under the <a href="https://github.com/ethereum/go-ethereum/tree/master/COPYING.LESSER">LGPL</a>
+and all frontend code is licensed under <a href="https://github.com/ethereum/go-ethereum/tree/master/COPYING">GPL</a>.
 </p>
 
 <p>