Bootstrap3でカラムを中央揃えにする

_columns.scss

/**
 * Bootstrap3でカラムを中央揃えにする
 * 
 */
@for $i from 1 through ($grid-columns / 2) {
  $columns: $i * 2;
  $offset: ($grid-columns - $columns) / 2;
  .col-xs-center-#{$columns} {
    @include make-xs-column-offset($offset);
    @include make-xs-column($columns);
  }
}
@for $i from 1 through ($grid-columns / 2) {
  $columns: $i * 2;
  $offset: ($grid-columns - $columns) / 2;
  .col-sm-center-#{$columns} {
    @include make-sm-column-offset($offset);
    @include make-sm-column($columns);
  }
}
@for $i from 1 through ($grid-columns / 2) {
  $columns: $i * 2;
  $offset: ($grid-columns - $columns) / 2;
  .col-md-center-#{$columns} {
    @include make-md-column-offset($offset);
    @include make-md-column($columns);
  }
}
@for $i from 1 through ($grid-columns / 2) {
  $columns: $i * 2;
  $offset: ($grid-columns - $columns) / 2;
  .col-lg-center-#{$columns} {
    @include make-lg-column-offset($offset);
    @include make-lg-column($columns);
  }
}