ENOMEM on server with 2GB of RAM

[tomasdev]

Steps to reproduce:

1. Create a VM or similar with 2GB of RAM
2. Create input-folder with 1000 jpegs of various sizes (in my sample I have files between 100kb and 1mb)
3. Run imagemin input-folder/* --out-dir=output-folder

Expected behavior:
Process finishes properly, as no single image requires a lot of memory.

Current output:
nodejs exits with a ENOMEM on child spawn after a bunch of images are processed (sort of random, but clearly depends on memory usage)

(tracked at nodejs/node#25382)

WORKAROUND
Create a bash script that runs imagemin for each file recursively in a folder