为什么Grails不能识别BuildStandalone？

Question

我有一个使用Grails Build Standalone plugin的Grails应用程序（2.3.6）。

myapp/grails-app/conf/BuildConfig.groovy：

plugins {
    runtime ":resources:1.2.7"
    compile 'org.grails.plugins:gson:1.1.4'
    compile ":standalone:1.2.3"
    build ":release:3.0.1"
    runtime ":cached-resources:1.0"
    compile ":cache-headers:1.0.4"
}

当我转到myapp并运行grails build-standalone myapp.jar --tomcat时，我得到了：

$ grails build-standalone myapp.jar --tomcat
|Loading Grails 2.3.6
|Configuring classpath
|Running pre-compiled script
|Script 'BuildStandalone' not found, did you mean:
    1) InstallDependency
    2) Stats
    3) CreateMultiProjectBuild_
    4) TestApp
    5) InstallPlugin
Please make a selection or enter Q to quit:

这里发生了什么？