message: web: Add waitFor before asserting on selector text
  This is an attempt to fix CI failures like this one:
diff: @@ -93,6 +93,8 @@ module('Acceptance | withdrawal', function (hooks) {
  assert
  .dom(postableSel(1, 1))
  .containsText(`Sufficient funds for claiming withdrawn tokens`);
  +
  + await waitFor(milestoneCompletedSel(1));
  assert.dom(milestoneCompletedSel(1)).containsText(`ETH balance checked`);
  await waitFor(postableSel(2, 0));
  @@ -440,7 +442,10 @@ module('Acceptance | withdrawal', function (hooks) {
  assert
  .dom(postableSel(1, 1))
  .containsText(`Sufficient funds for claiming withdrawn tokens`);
  +
  + await waitFor(milestoneCompletedSel(1));
  assert.dom(milestoneCompletedSel(1)).containsText(`ETH balance checked`);
  +
  await waitFor(postableSel(2, 0));
  assert
  .dom(postableSel(2, 0))
  