Served no longer fails due to server reuse

and no scalatest version gymnast...ics (1.9.1 across the board).

I'm not sure what kind of use this module sees, and I'm a bit new to Scalatest, but the current trait would fail all examples uses I've seen as it tries to reuse the server reference. This change hands out a fresh server via withFixture for each run; setups/teardowns included.