Improve rendering speed

See h5bp/html5-boilerplate#1874

Author: JimBobSquarePants

src/sass/partials/_helpers-visibility.scss

@@ -26,6 +26,7 @@
     overflow: hidden;
     padding: 0;
     position: absolute;
+    white-space: no-wrap;
     width: 1px;
     // Extends the .visuallyhidden class to allow the element to be focusable
     // when navigated to via the keyboard: h5bp.com/p