刚刚想上手Laravel，我是通过composer安装的，在Iterm2里出现：

 PHP Fatal error:  Allowed memory size of 536870912 bytes exhausted (tried to allocate 32 bytes) in phar:///usr/local/Cellar/composer/1.0.0-alpha8/libexec/composer.phar/src/Composer/DependencyResolver/RuleWatc hGraph.php on line 52

该如何解决？