ZOOKEEPER-3120: add NetBeans nbproject directory to .gitignore
ZOOKEEPER-3120: add NetBeans nbproject directory to .gitignore

Author: Enrico Olivelli <eolivelli@apache.org>

Reviewers: fangmin@apache.org, andor@apache.org

Closes #598 from eolivelli/fix/netbeans-nbproject

apache/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper,apache/zookeeper,hanm/zookeeper,apache/zookeeper,hanm/zookeeper,apache/zookeeper,hanm/zookeeper,hanm/zookeeper,maoling/zookeeper,apache/zookeeper,hanm/zookeeper,arshadmohammad/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper,apache/zookeeper,hanm/zookeeper,arshadmohammad/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper,apache/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper,hanm/zookeeper,maoling/zookeeper,apache/zookeeper,maoling/zookeeper,arshadmohammad/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper,hanm/zookeeper