Change default feed timeout

https://github.com/FreshRSS/FreshRSS/issues/1141

data/config.default.php

@@ -75,7 +75,7 @@ return array(
 		'cache_duration' => 800,
 
 		# SimplePie HTTP request timeout in seconds.
-		'timeout' => 10,
+		'timeout' => 15,
 
 		# If a user has not used FreshRSS for more than x seconds,
 		#	then its feeds are not refreshed anymore.