title: versions:display-plugin-updates does not understand maven-enforcer-plugin
body: <p>So, I'm trying to use the latest version of some plugins. Earlier I've used the prerequisites-tag but lots of resources (<a href="http://blog.peterlynch.ca/2009/12/robustly-enforcing-minimum-maven.html" rel="nofollow noreferrer" title="example">example</a>) say that it should be considered deprecated and that the maven-enforcer-plugin should be used instead. 
  this is my configuration:</p>
  
  <pre><code>&lt;plugin&gt;
    &lt;inherited&gt;true&lt;/inherited&gt;
    &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
    &lt;artifactId&gt;maven-enforcer-plugin&lt;/artifactId&gt;
    &lt;version&gt;1.3.1&lt;/version&gt;
    &lt;executions&gt;
      &lt;execution&gt;
        &lt;id&gt;enforce-maven-3&lt;/id&gt;
        &lt;goals&gt;
          &lt;goal&gt;enforce&lt;/goal&gt;
        &lt;/goals&gt;
        &lt;configuration&gt;
          &lt;rules&gt;
            &lt;requireMavenVersion&gt;
              &lt;version&gt;3.0.4&lt;/version&gt;
            &lt;/requireMavenVersion&gt;
          &lt;/rules&gt;
          &lt;fail&gt;true&lt;/fail&gt;
        &lt;/configuration&gt;
      &lt;/execution&gt;
    &lt;/executions&gt;
  &lt;/plugin&gt;
  </code></pre>
  
  <p>However, when I run <em>mvn versions:display-plugin-updates</em> I still get this text:</p>
  
  <pre><code>[ERROR] Project does not define required minimum version of Maven.
  [ERROR] Update the pom.xml to contain
  [ERROR]     &lt;prerequisites&gt;
  [ERROR]       &lt;maven&gt;3.0&lt;/maven&gt;
  [ERROR]     &lt;/prerequisites&gt;
  [INFO]
  [INFO] Require Maven 2.0.6 to use the following plugin updates:
  [INFO]   maven-jar-plugin ................................................ 2.4
  [INFO]   maven-shade-plugin ............................................ 1.7.1
  [INFO]
  [INFO] Require Maven 2.2.1 to use the following plugin updates:
  [INFO]   maven-jar-plugin ................................................ 2.6
  [INFO]
  [INFO] Require Maven 3.0 to use the following plugin updates:
  [INFO]   maven-shade-plugin .............................................. 2.3
  </code></pre>
  
  <p>Using the prerequisites-tag instead works.</p>