Migrate custom BEM to getBEM syntax

Author: anselmbradford

docs/_includes/footer.html

@@ -2,7 +2,7 @@
 
     <hr>
 
-    <div class="block block__sub ds-footer_content">
+    <div class="block block--sub ds-footer_content">
         <p>
             <small>
                 We need your help keeping the Design System accurate and up-to-date!

docs/_includes/redirect-banner.html

@@ -1,16 +1,16 @@
 <div
   id="redirect-banner"
-  class="block block__flush-top block__flush-bottom block__padded-top u-hidden"
+  class="block block--flush-top block--flush-bottom block--padded-top u-hidden"
 >
   <div class="m-global-banner">
-    <div class="wrapper wrapper__match-content">
-      <div class="m-notification m-notification__warning m-notification__visible">
-        <svg xmlns="http://www.w3.org/2000/svg" class="cf-icon-svg cf-icon-svg__warning-round" viewBox="0 0 17 20.4"><path d="M16.406 10.283a7.917 7.917 0 1 1-7.917-7.917 7.916 7.916 0 0 1 7.917 7.917zM9.48 14.367a1.003 1.003 0 1 0-1.004 1.003 1.003 1.003 0 0 0 1.004-1.003zM7.697 11.53a.792.792 0 0 0 1.583 0V5.262a.792.792 0 0 0-1.583 0z"/></svg>        <div class="m-notification_content">
-          <div class="h4 m-notification_message">
+    <div class="wrapper wrapper--match-content">
+      <div class="m-notification m-notification--warning m-notification--visible">
+        <svg xmlns="http://www.w3.org/2000/svg" class="cf-icon-svg cf-icon-svg__warning-round" viewBox="0 0 17 20.4"><path d="M16.406 10.283a7.917 7.917 0 1 1-7.917-7.917 7.916 7.916 0 0 1 7.917 7.917zM9.48 14.367a1.003 1.003 0 1 0-1.004 1.003 1.003 1.003 0 0 0 1.004-1.003zM7.697 11.53a.792.792 0 0 0 1.583 0V5.262a.792.792 0 0 0-1.583 0z"/></svg>        <div class="m-notification__content">
+          <div class="h4 m-notification__message">
             You’ve been redirected to this website from
             <span data-redirect="source-name"></span>.
           </div>
-          <p class="m-notification_explanation">
+          <p class="m-notification__explanation">
             The website you were trying to visit has been deprecated.
             Future updates will happen here.
           </p>