Fix icon button docs

docs/documentation/elements/button.html

@@ -226,7 +226,7 @@ doc-subtab: button
   </a>
   <a class="button">
   <span class="icon">
-    <i class="fa fa-header"></i>
+    <i class="fa fa-header fa-lg"></i>
   </span>
   </a>
 </p>
@@ -238,12 +238,12 @@ doc-subtab: button
   </a>
   <a class="button is-medium">
   <span class="icon">
-    <i class="fa fa-header"></i>
+    <i class="fa fa-header fa-lg"></i>
   </span>
   </a>
   <a class="button is-medium">
     <span class="icon is-medium">
-      <i class="fa fa-header"></i>
+      <i class="fa fa-header fa-2x"></i>
     </span>
   </a>
 </p>
@@ -255,17 +255,12 @@ doc-subtab: button
   </a>
   <a class="button is-large">
   <span class="icon">
-    <i class="fa fa-header"></i>
+    <i class="fa fa-header fa-lg"></i>
   </span>
   </a>
   <a class="button is-large">
     <span class="icon is-medium">
-      <i class="fa fa-header"></i>
-    </span>
-  </a>
-  <a class="button is-large">
-    <span class="icon is-large">
-      <i class="fa fa-header"></i>
+      <i class="fa fa-header fa-2x"></i>
     </span>
   </a>
 </p>