当我运行 composer.phar 安装时，一切似乎都很好：
→ sudo php composer.phar install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Nothing to install or update
Generating autoload files
Clearing the cache for the dev environment with debug true
Installing assets using the hard copy option
Installing assets for Symfony\Bundle\FrameworkBundle into web/bundles/framework
Installing assets for FOS\JsRoutingBundle into web/bundles/fosjsrouting
etc etc
但是现在，我想安装这个包：https://packagist.org/packages/knplabs/knp-paginator-bundle中的https://github.com/KnpLabs/KnpPaginatorBundle
所以我用新的 require 行更新了 composer.json 文件。
{
"require": {
"knplabs/knp-paginator-bundle": "v2.1"
}
}
（我已经尝试过packegist的每个版本的分页器，但仍然是同样的错误）
然后我尝试安装它：
→ sudo php composer.phar install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. Run update to update them.
Your requirements could not be resolved to an installable set of packages.
Problem 1
- Installation request for symfony/framework-standard-edition 2.1.x-dev -> satisfiable by symfony/framework-standard-edition[2.1.x-dev].
- symfony/framework-standard-edition 2.1.x-dev requires knplabs/knp-paginator-bundle v2.1 -> no matching package found.
Potential causes:
- A typo in the package name
- The package is not available in a stable-enough version according to your minimum-stability setting
see <https://groups.google.com/d/topic/composer-dev/_g3ASeIFlrc/discussion> for more details.
Read <http://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.
还有我当前 composer.json 的 symfony2 行：
"require": {
"php": ">=5.3.3",
"symfony/symfony": "2.1.*",
"doctrine/orm": ">=2.2.3,<2.4-dev",
"symfony/symfony": "2.1.x-dev" did not help
请问我该怎么办？