Fix test runner

[ErikSchierboom]

Closes #12

[ErikSchierboom]

@wneumann I'm trying to get the Swift test runner working and updated to the latest infrastructure for test runners. So far I've found and fixed some things, but now I'm getting something that I don't know how to fix.

If I run ./bin/run-in-docker.sh single-test-that-passes /home/erik/exercism-repos/swift-test-runner/tests/single-test-that-passes /home/erik/exercism-repos/swift-test-runner/tests/single-test-that-passes, the following error is displayed:

/solution: error: manifest parse error(s):
The operation could not be completed. (TSCBasic.Process.Error error 0.)
/opt/test-runner
{
  "message" : "\/solution: error: manifest parse error(s):\nThe operation could not be completed. (TSCBasic.Process.Error error 0.)\n",
  "status" : "error",
  "tests" : [

  ]
}

Do you have any idea how to fix this?

[ErikSchierboom]

(cc @exercism/swift)