Go back to single colon pseudo elements.

This is for backwards compatibility with the browsers we support in v3.

less/print.less

@@ -9,8 +9,8 @@
 
 @media print {
   *,
-  *::before,
-  *::after {
+  *:before,
+  *:after {
     color: #000 !important; // Black prints faster: h5bp.com/s
     text-shadow: none !important;
     background: transparent !important;
@@ -22,18 +22,18 @@
     text-decoration: underline;
   }
 
-  a[href]::after {
+  a[href]:after {
     content: " (" attr(href) ")";
   }
 
-  abbr[title]::after {
+  abbr[title]:after {
     content: " (" attr(title) ")";
   }
 
   // Don't show links that are fragment identifiers,
   // or use the `javascript:` pseudo protocol
-  a[href^="#"]::after,
-  a[href^="javascript:"]::after {
+  a[href^="#"]:after,
+  a[href^="javascript:"]:after {
     content: "";
   }