Example test runner is prone to exit status integer overflow

[Ambrose Bonnaire-Sergeant]

As in technomancy/leiningen#2718, returning sum of failures and errors can mean multiples of 256 test failures can return 0.

I recommend the example here change the final call to (System/exit (min 1 failures-and-errors)) so it's 0 for success and 1 for failure. (This is how we fixed this code in lein test).

[Ambrose Bonnaire-Sergeant]

Duplicate of #49