Fix build process: conflicting dependencies

[ongyx]

This PR fixes building piskel (using grunt desktop).

When building normally, grunt will show

>> TypeError: os.tmpDir is not a function

which causes the tasks defined after to not be registered:

Warning: Task "nwjs:windows" not found.

This is caused by outdated dependencies relying on os.tempDir, which was deprecated in Node 7. To fix this, just run patch_tempdir.sh at the root of this repo every time after you run npm install. Basically, it recurses through node_modules and replaces os.tempDir with os.tempdir.