Flexbox sticky footer (#2289)

* Remove sticky footer JavaScript

* Use flexbox to force footer to the bottom of every page

* Fix flexbox in Internet Explorer

assets/js/_main.js

@@ -3,18 +3,6 @@
    ========================================================================== */
 
 $(document).ready(function() {
-  // Sticky footer
-  var bumpIt = function() {
-    $("body").css("margin-bottom", $(".page__footer").outerHeight(true));
-  };
-
-  bumpIt();
-  $(window).resize(
-    jQuery.throttle(250, function() {
-      bumpIt();
-    })
-  );
-
   // FitVids init
   $("#main").fitVids();