如果你没有添加 GitHub 密钥的话，使用composer update会出现

Reading bower.json of bower-asset/jquery (1.11.3)
Could not fetch https://api.github.com/repos/jquery/jquery-dist/commits/1472290917f17af05e98007136096784f9051fab, please create a GitHub OAuth token to go over the API rate limit
Head to https://github.com/settings/tokens/new?scopes=repo&description=Composer+on+mazhenyus-MBP.lan+2017-06-20+1113
to retrieve a token. It will be stored in "/Users/mazhenyu/.composer/auth.json" for future use by Composer.
Token (hidden):

解决方法：

进入 https://github.com/settings/tokens 点击 「Generate new token」 新建一个 Token，输入描述，选择默认新建就行，然后就会得到一个 Token，然后把这个值粘贴过去就 OK 了。