Fix ERC721Token.sol code indent (#909)

contracts/token/ERC721/ERC721Token.sol

@@ -18,7 +18,7 @@ contract ERC721Token is ERC721, ERC721BasicToken {
   string internal symbol_;
 
   // Mapping from owner to list of owned token IDs
-  mapping (address => uint256[]) internal ownedTokens;
+  mapping(address => uint256[]) internal ownedTokens;
 
   // Mapping from token ID to index of the owner tokens list
   mapping(uint256 => uint256) internal ownedTokensIndex;