Fix page description (#1584)

Seems like the current text belong on the ```responsive-helpers``` page and not these generic helpers. I've cut a few words, but a better wording would probably be better.

docs/documentation/modifiers/helpers.html

@@ -10,7 +10,7 @@ doc-subtab: helpers
 <section class="section">
   <div class="container">
     <h1 class="title">Helpers</h1>
-    <h2 class="subtitle">You can apply <strong>responsive helper classes</strong> to almost any element, in order to alter its style based upon the browser's width.</h2>
+    <h2 class="subtitle">You can apply <strong>helper classes</strong> to almost any element, in order to alter its style.</h2>
     <hr>
     <table class="table is-bordered">
       <tbody>