Created gzip files are corrupt

[BrandonLive]

If I run zopfli.exe (with same default options, or explicitly specifying gzip), I get a functional gzip compressed file. If I use this task (default options, or explicitly specifying gzip), I get a non-functional file that is 11 bytes longer and fails gzip CRC checks.

The content of the working and non-working files appears identical except that the one generated by this task has errant newlines throughout (the zopfli.exe output has 3 lines, the grunt-zopfli output has 12. Looks like a problem in how you're writing the output stream to disk.

[BrandonLive]

It looks like this is an issue with how Node/child_process interacts with stdout on Windows. After trying a few things to make that work, I gave up and changed grunt-zopfli to just let zopfli create a new file (with ".gz" appended), then fs.rename that to destpath (after deleting any existing file there).