Add repository to package.json to stop npm error

Hi!

When installing DataTables from the repo with npm >v1.2.20, it'll WARN "No repository field." This small patch resolves that. (See https://www.npmjs.org/doc/files/package.json.html#repository or https://stackoverflow.com/questions/16827858/npm-warn-package-json-no-repository-field.)

I hope it's ok to propose this change against DataTables/DataTables -- I couldn't find a `package.json` in DataTablesSrc.

Thank you for your work!!
M