Improve usage of toString

contracts/token/ERC721/ERC721.sol

@@ -21,6 +21,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable
     using Address for address;
     using EnumerableSet for EnumerableSet.UintSet;
     using EnumerableMap for EnumerableMap.UintToAddressMap;
+    using Strings for uint256;
 
     // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
     // which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
@@ -153,7 +154,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable
             return string(abi.encodePacked(_baseURI, _tokenURI));
         }
         // If there is a baseURI but no tokenURI, concatenate the tokenID to the baseURI.
-        return string(abi.encodePacked(_baseURI, Strings.toString(tokenId)));
+        return string(abi.encodePacked(_baseURI, tokenId.toString()));
     }
 
     /**