v2.1.0: what keeps the cargo spinning is code from the beginning

Fixed:
  * Config featurespec on nightly cargos
    (aec98553362184517007c0e41e522e28c19bcd6d)
    (#113) (@jonasbb)

Changed:
  * cargo install-update --list now behaves like --list --all
    (NB: not breaking, since this was disallowed previously)
    (42d582a4c10ee0a1a13159a7a032b3df23694363)
    (#114)