title: ProGuard says Unsupported class version number [52.0] (maximum 51.0, Java 1.7) with sbt-proguard
body: <p>I'm on <strong>Mac OS X 10.9.2</strong> and <strong>sbt 0.13.3-SNAPSHOT</strong> (built from the sources), <strong>Java 8</strong> and <strong>sbt-proguard 0.2.2</strong> plugin.</p>
  
  <p><strong>sbt 0.13.3-SNAPSHOT</strong> </p>
  
  <pre><code>[jacek]&gt; sbtVersion
  [info] 0.13.3-SNAPSHOT
  </code></pre>
  
  <p><strong>Java 8</strong></p>
  
  <pre><code>$ /Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/bin/java -version
  java version "1.8.0"
  Java(TM) SE Runtime Environment (build 1.8.0-b132)
  Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode)
  </code></pre>
  
  <p><strong>project/plugins.sbt</strong></p>
  
  <pre><code>addSbtPlugin("com.typesafe.sbt" % "sbt-proguard" % "0.2.2")
  </code></pre>
  
  <p>When I ran <code>proguard:proguard</code> in sbt shell it blew up with the following exception:</p>
  
  <pre><code>[sbt-updates]&gt; show proguard:proguard
  [info] ProGuard, version 4.9
  [info] Reading program directory [/Users/jacek/oss/sbt-updates/target/scala-2.10/sbt-0.13/classes] (filtered)
  [info] Reading program jar [/Users/jacek/.ivy2/cache/org.scalaz/scalaz-concurrent_2.10/bundles/scalaz-concurrent_2.10-7.1.0-M6.jar] (filtered)
  [info] Reading program jar [/Users/jacek/.sbt/boot/scala-2.10.3/lib/scala-library.jar] (filtered)
  [info] Reading program jar [/Users/jacek/.ivy2/cache/org.scalaz/scalaz-core_2.10/bundles/scalaz-core_2.10-7.1.0-M6.jar] (filtered)
  [info] Reading program jar [/Users/jacek/.ivy2/cache/org.scalaz/scalaz-effect_2.10/bundles/scalaz-effect_2.10-7.1.0-M6.jar] (filtered)
  [info] Reading library jar [/Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/jre/lib/rt.jar]
  [error] Error: Can't read [/Library/Java/JavaVirtualMachines/jdk1.8.0.jdk/Contents/Home/jre/lib/rt.jar] (Can't process class [apple/applescript/AppleScriptEngine.class] (Unsupported class version number [52.0] (maximum 51.0, Java 1.7)))
  [trace] Stack trace suppressed: run last proguard:proguard for the full output.
  [error] (proguard:proguard) Proguard failed with exit code [1]
  [error] Total time: 16 s, completed Apr 19, 2014 2:27:56 PM
  </code></pre>
  
  <p>Why could be the reason for the error?</p>