Changed version file download URL in ispconfig_update.php to https.

Author: Till Brehm

server/scripts/ispconfig_update.php

@@ -91,7 +91,7 @@ function simple_query($query, $answers, $default)
 $method = simple_query('Select update method', array('stable', 'git-stable', 'git-master'), 'stable');
 
 if($method == 'stable') {
-	$new_version = @file_get_contents('http://www.ispconfig.org/downloads/ispconfig3_version.txt') or die('Unable to retrieve version file.');
+	$new_version = @file_get_contents('https://www.ispconfig.org/downloads/ispconfig3_version.txt') or die('Unable to retrieve version file.');
 	$new_version = trim($new_version);
 	if(version_compare($new_version, ISPC_APP_VERSION, '>')) {
 		passthru('/usr/local/ispconfig/server/scripts/update_stable.sh');