buildArgParser method
构建自己的命令参数
Implementation
@override
void buildArgParser(ArgParser argParser) {
argParser.addOption('path', abbr: 'p', help: 'Path of assets.');
argParser.addOption('output', abbr: 'o', help: 'Default output directory is "lib/generated.', defaultsTo: 'generated');
argParser.addOption('ignore', abbr: 'i', help: 'Ignored folders, separated by ",".');
}