Bugfix npm warn about "repositories" field

npm sends these warnings about the repositories field :

- npm WARN package.json sleep@1.1.2 'repositories' (plural) Not supported.
- npm WARN package.json Please pick one as the 'repository' field

As I don't know if the "repositories" field is needed for other purposes, I prefer adding a new "repository" field.

+ update version number
Merge pull request #7 from leny/master

Bugfix npm warn about "repositories" field