fix(docs): use window.execScript instead of window.eval on IE

IE's window.eval doesn't execute in the global context, so we have to
use window.execScript instead which works like window.eval on normal
browsers. However execScript throws an exception when an empty string is
passed in, so I created a workaround with a workaround.

docs/src/templates/doc_widgets.js

@@ -56,8 +56,13 @@
     element.append(tabs);
 
     var script = (exampleSrc.match(/<script[^\>]*>([\s\S]*)<\/script>/) || [])[1] || '';
+
     try {
-      window.eval(script);
+      if (window.execScript) { // IE
+        window.execScript(script || '"stupid IE!"'); // IE complains when evaling empty string
+      } else {
+        window.eval(script);
+      }
     } catch (e) {
       alert(e);
     }