ZOOKEEPER-3453: missing 'SET' in zkCli on windows

from #1195

Author: 慕华 <wrdfeng@gmail.com>

Reviewers: Andor Molnar <andor@apache.org>, Norbert Kalmar <nkalmar@apache.org>

Closes #1234 from wordfeng/patch-1

bin/zkCli.cmd

@@ -17,7 +17,7 @@ REM limitations under the License.
 setlocal
 call "%~dp0zkEnv.cmd"
 
-ZOO_LOG_FILE=zookeeper-%USERNAME%-cli-%COMPUTERNAME%.log
+set ZOO_LOG_FILE=zookeeper-%USERNAME%-cli-%COMPUTERNAME%.log
 
 set ZOOMAIN=org.apache.zookeeper.ZooKeeperMain
 call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.root.logger=%ZOO_LOG4J_PROP%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" -cp "%CLASSPATH%" %ZOOMAIN% %*