Make build compatiable with Gradle version 1.0-miestone-3

...r to run task of groovydoc

This change is to fix the following error to do build with   Gradle version 1.0-milestone-3 
FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':org.linkedin.zookeeper-cli-impl:groovydoc'.
Cause: org/slf4j/impl/StaticMarkerBinder
Cause: org.slf4j.impl.StaticMarkerBinder

I have tested the change in my foked repo:

linkedin-zookeeper hhan$ gradle -Prelease=true release
Working in release mode: 1.4.0
:org.linkedin.zookeeper-impl:compileJava UP-TO-DATE
:org.linkedin.zookeeper-impl:compileGroovy UP-TO-DATE
:org.linkedin.zookeeper-impl:processResources UP-TO-DATE
:org.linkedin.zookeeper-impl:classes UP-TO-DATE
:org.linkedin.zookeeper-impl:jar
:org.linkedin.zookeeper-cli-impl:compileJava UP-TO-DATE
:org.linkedin.zookeeper-cli-impl:compileGroovy
:org.linkedin.zookeeper-cli-impl:processResources UP-TO-DATE
:org.linkedin.zookeeper-cli-impl:classes
:org.linkedin.zookeeper-cli-impl:jar
:org.linkedin.zookeeper-cli:package-assemble
:org.linkedin.zookeeper-cli:package
:org.linkedin.zookeeper-cli:uploadReleaseMaster
:org.linkedin.zookeeper-cli:release
:org.linkedin.zookeeper-cli-impl:groovydoc
log4j:WARN No appenders could be found for logger (org.gradle.api.internal.project.ant.AntLoggingAdapter).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
:org.linkedin.zookeeper-cli-impl:groovydocJar
:org.linkedin.zookeeper-cli-impl:sourcesJar
:org.linkedin.zookeeper-cli-impl:uploadReleaseMaster
:org.linkedin.zookeeper-cli-impl:release
:org.linkedin.zookeeper-impl:javadoc
:org.linkedin.zookeeper-impl:javadocJar
:org.linkedin.zookeeper-impl:sourcesJar
:org.linkedin.zookeeper-impl:uploadReleaseMaster
:org.linkedin.zookeeper-impl:release
:org.linkedin.zookeeper-server:package-assemble
:org.linkedin.zookeeper-server:package
:org.linkedin.zookeeper-server:uploadReleaseMaster
:org.linkedin.zookeeper-server:release

BUILD SUCCESSFUL

Total time: 15.71 secs