修正一些存在的警告错误

library/think/cache/driver/Memcache.php

@@ -24,6 +24,7 @@ class Memcache
         'timeout'    => 0, // 超时时间（单位：毫秒）
         'persistent' => true,
         'length'     => 0,
+        'prefix'     => '',
     ];
 
     /**
@@ -51,7 +52,7 @@ class Memcache
         foreach ((array) $hosts as $i => $host) {
             $port = isset($ports[$i]) ? $ports[$i] : $ports[0];
             $this->options['timeout'] > 0 ?
-            $this->handler->addServer($host, $port, $this->options['persistent'], 1, $this->options['timeout']) : 
+            $this->handler->addServer($host, $port, $this->options['persistent'], 1, $this->options['timeout']) :
             $this->handler->addServer($host, $port, $this->options['persistent'], 1);
         }
     }

library/think/cache/driver/Memcached.php

@@ -23,6 +23,7 @@ class Memcached
         'expire'  => 0,
         'timeout' => 0, // 超时时间（单位：毫秒）
         'length'  => 0,
+        'prefix'  => '',
     ];
 
     /**

library/think/cache/driver/Redis.php

@@ -30,6 +30,7 @@ class Redis
         'expire'     => false,
         'persistent' => false,
         'length'     => 0,
+        'prefix'     => '',
     ];
 
     /**

library/think/cache/driver/Sae.php

@@ -28,6 +28,7 @@ class Sae
         'timeout'    => false,
         'persistent' => false,
         'length'     => 0,
+        'prefix'     => '',
     ];
 
     /**