no storeInflightPackets when persistClient
Bumped browserify, mqtt and st dependencies.
Update offline packets with messageId === 0.

Closes #174.
Merge branch 'master' into fix_173
remove useless storeInflightPackets
use uuid for server level messageId
Merge pull request #175 from mocheng/fix_173

no storeInflightPackets when persistClient
generate unique id by shortid
Merge pull request #176 from mocheng/fix_172

use unique id for server level messageId
Removed node-uuid in favor of shortid.