UP-4170 allow Ant 1.9.3+.

While Ant `1.8.2` has historically been required for uPortal, Ant `1.9.3` seems to work.

See also [UP-4170](https://issues.jasig.org/browse/UP-4170).

Updates the build to not artificially fail on Ant 1.9.3 and the documentation to suggest 1.9.3 and later.  Leaves in explicit reference to 1.8.2 so that if (when) some post 1.9.3 version of Ant doesn't work again, there's the ready indication that 1.8.2 might be a safe Ant version to fall back to.

In practice adopters are going to try to use Ant 1.9.3 because that's an easy latest release to have handy from such things as Ubuntu package management.  This change should make uPortal less difficult to install for the happy path where the system version of Ant just works.