Error trying to use getdown-ant

Following the instructions I'm having this error when trying to run the getdown ant task:
`java.lang.NoClassDefFoundError: com/threerings/getdown/tools/Digester`

As per documentation:
```
<taskdef name="digest" classname="com.threerings.getdown.tools.DigesterTask"
					 classpath="../Tools/getdown-ant-1.8.7.jar"/>
<digest appdir="dist"/>
```