fix issue http://bit.ly/16hA0B5 .Replace zipstream by grunt-contrib-compress

Hello,

I fix the issue I had when running grunt default task:
"(node) warning: Recursive process.nextTick detected. This will break in the next version of node. Please use setImmediate for recursive deferral."

I seems the zipstream module no longer works with node 0.10 . Was suggested to use grunt-contrib-compress

Thanks