Using: `"grunt-contrib-imagemin" : "~0.4.1",` See https://core.trac.wordpress.org/ticket/25169

gistfile1.txt

> optipng-bin@0.3.1 postinstall C:\xampp\htdocs\develop.wp.nw\node_modules\grunt-contrib-imagemin\node_modules\optipng-bin
> node lib/check.js

  pngquant.exe: downloading [===================] 100% 0.0s


  gifsicle.exe: downloading [===================] 100% 0.0s


  optipng.exe: downloading [====               ] 25% 0.9s✗ pre-build test failed, compiling from source...
✗ building is not supported on win32
  optipng.exe: downloading [========           ] 47% 0.5s✓ pre-build test passed successfully
  optipng.exe: downloading [===================] 100% 0.0s


✗ pre-build test failed, compiling from source...

C:\xampp\htdocs\develop.wp.nw\node_modules\grunt-contrib-imagemin\node_modules\optipng-bin\lib\check.js:11
            throw new Error('building is not supported on ' + process.platform
                  ^
Error: building is not supported on win32
    at C:\xampp\htdocs\develop.wp.nw\node_modules\grunt-contrib-imagemin\node_modules\optipng-bin\lib\check.js:11:19
    at ChildProcess.<anonymous> (C:\xampp\htdocs\develop.wp.nw\node_modules\grunt-contrib-imagemin\node_modules\optipng-bin\node_modules\bin-wrapper\b
in-wrapper.js:174:16)
    at ChildProcess.EventEmitter.emit (events.js:98:17)
    at Process.ChildProcess._handle.onexit (child_process.js:789:12)
  libjpeg-62.dll: downloading [===================] 100% 0.0s


  libjpeg-62.dll: downloading [===================] 100% 0.0s


✓ pre-build test passed successfully
npm ERR! weird error 8
npm ERR! not ok code 0