title: Keep subviews as original dimensions in UIStackView
body: <p>Currently I'm trying to make 3 buttons in a horizontal group of 3 that have equal spacing</p>
  
  <pre><code>UIStackView * menuButtons = [[UIStackView alloc] initWithFrame:CGRectMake(0, 0, 60, 16)];
    menuButtons.axis = UILayoutConstraintAxisHorizontal;
    menuButtons.alignment = UIStackViewAlignmentBottom;
    menuButtons.spacing = 6;
    menuButtons.distribution = UIStackViewDistributionEqualSpacing;
  
  UIButton* btnOne = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 16, 16)];
  UIButton* btnTwo = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 16, 16)];
  UIButton* btnThree = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 16, 16)];
  
    [menuButtons addArrangedSubview:btnOne];
    [menuButtons addArrangedSubview:btnTwo];
    [menuButtons addArrangedSubview:btnThree];
  </code></pre>
  
  <p>ive noticed when I inspect the frame of the button views after adding them to my stackview programatically, they all show different sizes than originally set, when I expect them all to still be 16</p>
  
  <p>ie: btnOne CGSize(17, 16), btnTwo CGSize(23.5, 23,5), btnThree CGSize(21.3, 21.3)</p>
  
  <p>I don't understand why this happens, and I've tried all the distributions but I can't figure this out when I'm not setting the frames on these views anywhere else</p>