Change note.html shortcode class names to fit BEM scheme.

Author: pyrrho

layouts/shortcodes/note.html

@@ -1,6 +1,6 @@
-<div class="note">
+<div class="blocknote">
   {{ if .Get "title" }}
-    <div class="title">{{ with .Get "title" }}{{ markdownify . }}{{ end }}</div>
+    <div class="blocknote__title">{{ with .Get "title" }}{{ markdownify . }}{{ end }}</div>
   {{ end }}
   {{ .Inner }}
 </div>