Fix docs for Math.log256 (#3916)

contracts/utils/math/Math.sol

@@ -324,7 +324,7 @@ library Math {
     }
 
     /**
-     * @dev Return the log in base 10, following the selected rounding direction, of a positive value.
+     * @dev Return the log in base 256, following the selected rounding direction, of a positive value.
      * Returns 0 if given 0.
      */
     function log256(uint256 value, Rounding rounding) internal pure returns (uint256) {