Update 10gen package name

The modern 10gen dists of mongodb use teh 'mongodb-org' package names: http://downloads-distro.mongodb.org/repo/ubuntu-upstart/dists/dist/10gen/binary-amd64/

This is also what the Ubuntu installation guide suggests: http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/
Merge pull request #287 from tgwizard/patch-1

Update 10gen package name