title: Your requirements could not be resolved to an installable set of packages
body: <p>Sorry for duplication of this question with another one. I can't solve my problem.</p>
  
  <p>I am working on a project based on <a href="http://socketo.me" rel="noreferrer"><code>Ratchet</code></a>. I am trying to run the <a href="http://socketo.me/docs/push" rel="noreferrer"><code>Push Integration</code></a> example. So, in order to run, I should use composer to get some dependencies. I make a composer.json file like below:</p>
  
  <pre><code>{
      "autoload": {
          "psr-0": {
              "MyApp": "src"
          }
      },
      "require": {
          "cboden/ratchet": "0.3.*",
          "react/zmq": "0.2.*|0.3.*"
      }
  }
  </code></pre>
  
  <p>When I execute composer on it, below error occurrs:</p>
  
  <pre><code>Loading composer repositories with package information
  Installing dependencies (including require-dev)
  Your requirements could not be resolved to an installable set of packages.
  
    Problem 1
      - react/zmq v0.3.0 requires ext-zmq * -&gt; the requested PHP extension zmq is missing from your system.
      - react/zmq v0.2.0 requires ext-zmq * -&gt; the requested PHP extension zmq is missing from your system.
      - Installation request for react/zmq 0.2.*|0.3.* -&gt; satisfiable by react/zmq[v0.2.0, v0.3.0].
  </code></pre>
  
  <p>Below you can find composer.json of <code>Ratchet</code> and <code>ZMQ</code>:</p>
  
  <p>ZMQ:</p>
  
  <pre><code>{
      "name": "react/zmq",
      "description": "ZeroMQ bindings for React.",
      "keywords": ["zmq", "zeromq"],
      "license": "MIT",
      "require": {
          "php": "&gt;=5.4.0",
          "ext-zmq": "*",
          "evenement/evenement": "~2.0",
          "react/event-loop": "0.4.*"
      },
      "require-dev": {
          "ext-pcntl": "*"
      },
      "autoload": {
          "psr-0": { "React\\ZMQ": "src" }
      },
      "extra": {
          "branch-alias": {
              "dev-master": "0.4-dev"
          }
      }
  }
  </code></pre>
  
  <p>Ratchet:</p>
  
  <pre><code>{
      "name": "cboden/ratchet"
    , "type": "library"
    , "description": "PHP WebSocket library"
    , "keywords": ["WebSockets", "Server", "Ratchet", "Sockets"]
    , "homepage": "http://socketo.me"
    , "license": "MIT"
    , "authors": [
          {
              "name": "Chris Boden"
            , "email": "cboden@gmail.com"
            , "role": "Developer"
          }
      ]
    , "support": {
          "forum": "https://groups.google.com/forum/#!forum/ratchet-php"
        , "issues": "https://github.com/ratchetphp/Ratchet/issues"
        , "irc": "irc://irc.freenode.org/reactphp"
      }
    , "autoload": {
          "psr-0": {
              "Ratchet": "src"
          }
      }
    , "require": {
          "php": "&gt;=5.3.9"
        , "react/socket": "0.3.*|0.4.*"
        , "guzzle/http": "~3.6"
        , "symfony/http-foundation": "~2.2"
        , "symfony/routing": "~2.2"
      }
  }
  </code></pre>
  
  <p>What is wrong? Please give me a solution. 
  Thanks in advance :)</p>