zlib deflate results in a memory leak #8871

• Version:6.7.0
• Platform:Darwin ITs-MacBook-Pro.local 15.6.0 Darwin Kernel Version 15.6.0: Thu Jun 23 18:25:34 PDT 2016; root:xnu-3248.60.10~1/RELEASE_X86_64 x86_64
• Subsystem:zlib

I'm using the graylog2 package for logging, and we ran into significant memory leak issues.
After tracking it down, I found zlib.deflate is the source of the issue.
The issue is magnified when running code inside of docker with the latest node distribution.

Running the below code on my macbook pro results in the memory spiking to ~3GB, then released down to 600MB.
Running the code in the latest node docker distro results in memory spiking to ~3GB, and it is never released.

let zlib = require('zlib');

let message = {
  some:"data"
};
let payload = new Buffer(JSON.stringify(message));

for(var i =0; i < 30000; ++i){
  zlib.deflate(payload, function (err, buffer) {
  });
}

setTimeout(()=>{}, 2000000);

This has resulted in our docker containers crashing due to memory exhaustion.