using group.children instead of the query selector

Unfortunately, there isn't a querySelectorAll that works for getting the immediate children of an element. :scope would work but it has limited support and I dont want to add a polyfill. Using .children and then filtering out the things that don't have a pfe-heading attribute should do the trick.

Fixes #314

Author: kylebuch8

elements/pfe-content-set/demo/index.html

@@ -15,7 +15,8 @@
           '../../../themes/cp-theme/cp-theme.umd.js',
           '../pfe-content-set.umd.js',
           '../../pfe-tabs/pfe-tabs.umd.js',
-          '../../pfe-accordion/pfe-accordion.umd.js'
+          '../../pfe-accordion/pfe-accordion.umd.js',
+          '../../pfe-cta/pfe-cta.umd.js'
         ]);
     </script>
     <noscript>
@@ -36,6 +37,7 @@ <h3>Container max: 500px</h3>
         <pfe-content-set-group>
           <h2 pfe-heading>Heading 1</h2>
           <p>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore </p>
+          <pfe-cta priority="primary" color="base" on="dark"><a href="#">Primary</a></pfe-cta>
         </pfe-content-set-group>
         <pfe-content-set-group>
           <h2 pfe-heading>Heading 2</h2>
@@ -98,6 +100,7 @@ <h2>On desktop, example below should render as tabs (default style):</h2>
             <h2 pfe-heading>Heading 1 Foo</h2>
             <p>Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</p>
             <p>Consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua</p>
+            <pfe-cta priority="primary" color="base" on="dark"><a href="#">Primary</a></pfe-cta>
           </pfe-content-set-group>
           <pfe-content-set-group>
             <h2 pfe-heading>Heading 2</h2>