Fix some bugs with new PHP versions

Looks like the validatorIp got some problem related to some PHP versions.
According to 3v4l.org behavior are quite different for reserved IPv4 224.0.0.0/4 https://3v4l.org/cAdWZ
Instead of keeping the failing test while PHP fix the problem, I've switched to 240.0.0.1 IP which is working.

I've also submitted a bug to PHP to see what could be wrong with 224.0.0.0 IPs.
https://bugs.php.net/bug.php?id=73653

Author: j0k3r

.travis.yml

@@ -14,7 +14,6 @@ php:
 matrix:
     fast_finish: true
     allow_failures:
-        - php: 7.1
         - php: hhvm
         - php: nightly
 

lib/plugin/sfPearFrontendPlugin.class.php

@@ -3,7 +3,7 @@
 /*
  * This file is part of the symfony package.
  * (c) Fabien Potencier <fabien.potencier@symfony-project.com>
- * 
+ *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
@@ -46,7 +46,7 @@ public function _display($text)
 
   protected function splitLongLine($text)
   {
-    $lines = '';
+    $lines = array();
     foreach (explode("\n", $text) as $longline)
     {
       foreach (explode("\n", wordwrap($longline, 62)) as $line)

test/unit/validator/sfValidatorIpTest.php

@@ -41,7 +41,7 @@
 
 $invalidReservedV4Ips = array(
   '0.0.0.0',
-  '224.0.0.1',
+  '240.0.0.1',
   '255.255.255.255'
 );