port to time-1.5

ehem... you might want to consider using pvp ;-)
Ah, I understand.

It looks like none of the cases is ideal:

* `default: True`: Installing this package as the first one will install `time-1.5`, breaking later installed packages that require `time-1.4`.
* `default: False`: Installing this package as the first one will install `time-1.4`, breaking later installed packages that require `time-1.5`.

At least the chance that somebody goes ahead and installs `iso8601-time` out of fun is quite low, it will probably be installed as a dependency of some other package or into an existing package db, so that the other packages will determine the `time` version before `iso8601-time` has to.

Facing an arbitrary choice, let's go with `default: True` because cabal also installs the most recent version when it is free of constraints.