message: Fixes grammar in initialization error
diff: @@ -247,7 +247,7 @@ class TestRunner {
  if (err.type === 'ProcessTerminatedError') {
  console.error(
  'A worker process has quit unexpectedly! ' +
  - 'Most likely this an initialization error.',
  + 'Most likely this is an initialization error.',
  );
  process.exit(1);
  }
  