duo: Use win-fork rather than child_process.spawn

See:

 * https://github.com/duojs/duo/pull/118#discussion_r15720060
* https://github.com/duojs/duo/issues/221
Fixed minor typo
Safer way to check if a path is a file

Directories can contain `.` too.
Fixed path root checking in findroot()
Fixed npm warn for missing repository field on package.json
Merge pull request #242 from ruyadorno/fix-npm-repository-warn

Fixes a npm warning
Merge pull request #216 from kevva/is-file

Safer way to check if a path is a file
Use path.sep when splitting cwd.
Merge pull request #241 from darsain/fix/findroot

Fixed hanging on windows when there is no manifest
deps: Replace win-fork with cross-spawn
Merge pull request #236 from pborreli/patch-1

Fixed minor typo
Merge pull request #223 from stephenmathieson/add/windows-subcommand-support

duo: Use win-fork rather than child_process.spawn
Add description, homepage and license

https://www.npmjs.org/doc/files/package.json.html
Merge pull request #249 from shinnn/master

Add description, homepage and license