Allow cnpm to be used instead of npm on Windows

[TooBug]

cnpm is a replacement tool of npm which optimized the install speed. BTW, it uses a Chinese mirror by default.

The structure of node_modules is quite different when modules are installed with cnpm. (It uses some soft links.)

The installation of cnpm is:

npm install -g cnpm

When package apps, electron-packager hangs. The log stopped by this:

electron-packager Ignored paths based on the out param: +3ms [ '/Users/TooBug/app-darwin-ia32',
  '/Users/TooBug/app-darwin-x64',
  '/Users/TooBug/app-darwin-armv7l',
  '/Users/TooBug/app-linux-ia32',
  '/Users/TooBug/app-linux-x64',
  '/Users/TooBug/app-linux-armv7l',
  '/Users/TooBug/app-mas-ia32',
  '/Users/TooBug/app-mas-x64',
  '/Users/TooBug/app-mas-armv7l',
  '/Users/TooBug/app-win32-ia32',
  '/Users/TooBug/app-win32-x64',
  '/Users/TooBug/app-win32-armv7l' ]

And the template folder of app is keeping increase, never stops.

I guess the problem occurs on the npm prune step.

related issue: cnpm/npminstall#155

[malept]

Does cnpm prune --production exist? If so, if you modify Electron Packager to use that command instead of npm prune --production, does it still hang?

[TooBug]

Yes, cnpm do has the same prune command. How can I force electron-packager to use that command?

[malept]

Electron Packager needs to be changed to be able to specify a custom command as the package manager, in order to run the "prune devDependencies" command. (And also an npm install command in the testsuite.)

It should be called packageManager in the API, and --package-manager in the CLI. The default value should be npm. It should fail with a nice error message if the specified package manager either does not exist or is not an executable file.

I am happy to review pull requests that implement this (and, obviously, follow the contributing guidelines).

[malept]

I am having a really difficult time getting cnpm to be called correctly on Windows, for some reason. This is the error I keep getting from both child_process.exec and spawn-rx.spawnPromise, despite running npm install -g cnpm and verifying that it creates a cnpm.cmd file:

Error: The filename, directory name, or volume label syntax is incorrect.

Since Windows is not my area of expertise, I'm inclined to only implement cnpm support for Linux/macOS and wait for someone to file a PR to get this working correctly on Windows. It will raise an error if cnpm is selected on Windows in the meantime.