Set minimum required version of PHP to 5.6

Author: Naktibalda

install.html

@@ -7,7 +7,7 @@
     <div class="pull-right well">
       <h4>Requirements</h4>
       <strong>
-        <div>PHP 5.4+</div>
+        <div>PHP 5.6+</div>
         <div>CURL enabled</div>
       </strong>
     </div>