Ethereum/Solidity toLower() equivalent, to transform strings to lowercase

StringToLower.sol

pragma solidity ^0.4.11;

contract StringToLower {
	function _toLower(string str) internal returns (string) {
		bytes memory bStr = bytes(str);
		bytes memory bLower = new bytes(bStr.length);
		for (uint i = 0; i < bStr.length; i++) {
			// Uppercase character...
			if ((bStr[i] >= 65) && (bStr[i] <= 90)) {
				// So we add 32 to make it lowercase
				bLower[i] = bytes1(int(bStr[i]) + 32);
			} else {
				bLower[i] = bStr[i];
			}
		}
		return string(bLower);
	}
}

this is solidity 0.5 version

function _toLower(string memory str) internal pure returns (string memory) {
        bytes memory bStr = bytes(str);
        bytes memory bLower = new bytes(bStr.length);
        for (uint i = 0; i < bStr.length; i++) {
            // Uppercase character...
            if ((uint8(bStr[i]) >= 65) && (uint8(bStr[i]) <= 90)) {
                // So we add 32 to make it lowercase
                bLower[i] = bytes1(uint8(bStr[i]) + 32);
            } else {
                bLower[i] = bStr[i];
            }
        }
        return string(bLower);
    }