Announce plugin doesn't work

I’m trying to gradle Announce plugin to get notification, but it doesn’t work well.

First, I installed growl on my mac.

Then, I write a simple build.gradle:

apply plugin: 'announce' 

task hello { 
        doLast {
            println "Hello, world!"
            announce.announce("helloWorld completed!", "growl")

Finally, I run the task gradle hello in iterm2.

In principle, my should receive a notification from growl. But I don’t receive anything. Can anyone help me? Thanks.