Update arc72 indexer url for mainnet (#5)

Author: xarmian

docs/developers/tools.md

@@ -16,7 +16,7 @@ In order to make development easier there are a number of ecosystem specific too
        * [https://testnet-api.voi.nodely.dev](https://testnet-api.voi.nodely.dev)
        * [https://testnet-idx.voi.nodely.dev](https://testnet-idx.voi.nodely.dev)
 * Smart Assets NFT Indexer
-    * [https://arc72-idx.voirewards.com/api-docs/](https://arc72-idx.voirewards.com/api-docs)
+    * [https://arc72-voi-mainnet.nftnavigator.xyz/api-docs](https://arc72-voi-mainnet.nftnavigator.xyz/api-docs)
 * Smart Assets interaction library
     * [https://github.com/temptemp3/ulujs](https://github.com/temptemp3/ulujs)
 * Block Explorers