内存溢出异常：
Fatal error: Allowed memory size of 2147483648 bytes exhausted (tried to allocate 4096 bytes) in phar://D:/composer/composer.phar/src/Composer/DependencyResolver/RuleWatchGraph.php on line 52
Check https://getcomposer.org/doc/articles/troubleshooting.md#memory-limit-errors for more info on how to handle out of memory errors.
解决方案：
1、查看你设置的memory_limit的值
php -r "echo ini_get('memory_limit').PHP_EOL;"
2、在php.ini中设置menory_limit的值为-1（未限制）
3、在命令行中执行
php -d memory_limit=-1 d:/composer/composer.phar
注：d:/compser/composer.phar为你的composer.phar文件的绝对路径