source/scss/main.scss: Apply blockquote style to all blockquotes

Bootstrap's default only styles blockquote tags that also have the
class "blockquote". As Hugo's Markdown syntax for blockquotes only
produces bare blockquote tags, we should apply the same style to
those as well, as this is most likely what users expect.

Note: there seems to be a regression in the style used in v4 Alpha
6 as compared to v4 Beta 1. Need to follow that up, but for now I
will just copy the style verbatim.

See: https://github.com/alanorth/hugo-theme-bootstrap4-blog/issues/50

source/scss/main.scss

@@ -1,6 +1,6 @@
 /*
- * From the Bootstrap v4 alpha blog example
- * See: http://v4-alpha.getbootstrap.com/examples/blog/blog.css
+ * From the Bootstrap 4.0 blog example
+ * See: https://getbootstrap.com/docs/4.0/examples/blog/blog.css
  */
 
 /*
@@ -173,10 +173,8 @@ section + #disqus_thread {
 // style all blockquotes, not just Bootstrap's default of class="blockquote"
 // see: node_modules/bootstrap/scss/_type.scss
 article blockquote {
-  padding: ($spacer / 2) $spacer;
   margin-bottom: $spacer;
   font-size: $blockquote-font-size;
-  border-left: $blockquote-border-width solid $blockquote-border-color;
 }
 
 // ensure that code text doesn't butt up against the background change