bugfix ZookeeperShardState:IOException is never thrown

ZookeeperSharedState can't be compiled because it has unnecessary try-catch clause.

```
[info] Compiling 28 Java sources to /home/vagrant/kinesis-storm-spout/target/scala-2.10/classes...
[error] /home/vagrant/kinesis-storm-spout/src/main/java/com/amazonaws/services/kinesis/stormspout/state/zookeeper/ZookeeperShardState.java:67: error: exception IOException is never thrown in body of corresponding try statement
[error]         } catch (IOException e) {
[error]           ^
[error] 1 error
[error] (compile:compile) javac returned nonzero exit code
```