Horizontal rule hard-coded margin introduced in Beta

Created by: ernestbofill

Since the beta version of Bootstrap, the margin of the horizontal rule defined in _type.scss is a hard-coded making it difficult to customize.

In latest alpha:

// type.scss line 53:
hr {
  margin-top: $spacer-y;
  margin-bottom: $spacer-y;
  //...
}

In beta:

// type.scss line 53:
hr {
  margin-top: 1rem;
  margin-bottom: 1rem;
  //...
}

I would like this margin to use a variable so that it can be customized.