Include ant CompileTask in maven jar to fix issue 121

Fixes issue #121 

To verify this fix, simply run mvn clean install, then use the produced jar in an ant build file to be able to run CompileTask.

    <taskdef name="closure" classname="com.google.javascript.jscomp.ant.CompileTask" classpathref="/path/to/jar"/>
    <closure languageIn="ECMASCRIPT5" compilationLevel="simple" debug="true" output="/path/to/file.min.js">
      <sources dir="/path/to">
        <file name="file.js"/>
      </sources>
    </closure>


Ping @jpitz to review