message: fix exception test
diff: import test from 'ava';
  import ValidatorException from './../src/exceptions/validatorException';
  -test('messages are branded by the plugin name', t => {
  +test('exception messages are branded by the plugin name', t => {
  const ex = new ValidatorException('Something went wrong.');
  - t.is(ex.message, 'Error: [vee-validate]: Something went wrong.');
  + t.is(ex.message, '[vee-validate]: Something went wrong.');
  });
  