title: addSbtPlugin(...) cause eviction warning but 'evicted' command shows nothing
body: <p>With sbt 1.2.7 and <code>sbt-pgp</code> plugin, sbt shows eviction warning.</p>
  
  <pre><code>$ rm -rf target project/target &amp;&amp; sbt ";clean;compile"
  [info] Loading global plugins from /home/kbigwheel/.sbt/1.0/plugins
  [info] Loading project definition from /home/kbigwheel/code/_investigation/2019-01-04-evicted-warning-investigation-3/plugins/project/project
  [info] Loading settings for project plugins-build from test.sbt ...
  [info] Loading project definition from /home/kbigwheel/code/_investigation/2019-01-04-evicted-warning-investigation-3/plugins/project
  [info] Updating ProjectRef(uri("file:/home/kbigwheel/code/_investigation/2019-01-04-evicted-warning-investigation-3/plugins/project/"), "plugins-build")...
  [info] Done updating.
  [warn] There may be incompatibilities among your library dependencies; run 'evicted' to see detailed eviction warnings.
  [info] Loading settings for project plugins from build.sbt ...
  [info] Set current project to plugins (in build file:/home/kbigwheel/code/_investigation/2019-01-04-evicted-warning-investigation-3/plugins/)
  [success] Total time: 0 s, completed 2019/01/05 13:27:05
  [info] Updating ...
  [info] Done updating.
  [success] Total time: 0 s, completed 2019/01/05 13:27:05
  </code></pre>
  
  <p>However, evicted command shows nothing.</p>
  
  <pre><code>$ sbt evicted
  [info] Loading global plugins from /home/kbigwheel/.sbt/1.0/plugins
  [info] Updating ProjectRef(uri("file:/home/kbigwheel/.sbt/1.0/plugins/"), "global-plugins")...
  [info] Done updating.
  [info] Loading project definition from /home/kbigwheel/proj-name/project/project
  [info] Updating ProjectRef(uri("file:/home/kbigwheel/proj-name/project/project/"), "proj-name-build-build")...
  [info] Done updating.
  [info] Loading settings for project proj-name-build from test.sbt ...
  [info] Loading project definition from /home/kbigwheel/proj-name/project
  [info] Updating ProjectRef(uri("file:/home/kbigwheel/proj-name/project/"), "proj-name-build")...
  [info] Done updating.
  [warn] There may be incompatibilities among your library dependencies; run 'evicted' to see detailed eviction warnings.
  [info] Set current project to proj-name (in build file:/home/kbigwheel/proj-name/)
  [info] Updating ...
  [info] Done updating.
  [success] Total time: 0 s, completed 2019/01/05 13:52:46
  </code></pre>
  
  <h2>Additional Info</h2>
  
  <ol>
  <li>With sbt 1.1.6, no warnings</li>
  <li>With sbt 1.2.0, warning occured</li>
  <li>With <code>sbt-sonatype</code>, no warnings</li>
  <li>With <code>sbt-native-packager</code>, warning occured</li>
  </ol>
  
  <p>Therefore, this warning must happens with specific plugin and sbt 1.2.0 or higher.</p>
  
  <p>source to reproduce: <a href="https://github.com/bigwheel/sbt-unknown-evicted-warning" rel="noreferrer">https://github.com/bigwheel/sbt-unknown-evicted-warning</a></p>
  
  <p>Why the warning shows ? and how to resolve this message ?</p>