Make it clean that only PHP 5.6 is supported

Author: Naktibalda

_includes/phar.html

@@ -37,7 +37,7 @@ <h4 class="panel-title">
     <div class="panel-heading" role="tab" id="headingTwo">
       <h4 class="panel-title">
         <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseTwo" aria-expanded="true" aria-controls="collapseTwo">
-        Install Phar for PHP 5.x
+        Install Phar for PHP 5.6
         </a>
       </h4>
       </div>