package.json: use “repository” instead of “repositories”

This commit fixes the following warning in projects depending on this
one:

    npm WARN package.json autoquit@0.1.4 'repositories' (plural) Not supported.
    npm WARN package.json Please pick one as the 'repository' field
Merge pull request #1 from herzi/master

package.json: use “repository” instead of “repositories”