Support PHP 5.3

Short array syntax wasn't introduced until 5.4.
I'm all for advancement, but I'm opposed to breaking backward
compatibility for syntactic sugar :)

Fixes #38

src/Adapters/Apc.php

@@ -603,7 +603,7 @@ protected function apcu_fetch($key, &$success = null)
         if (is_array($key)) {
             $nums = array_filter($key, 'is_numeric');
             if ($nums) {
-                $values = [];
+                $values = array();
                 foreach ($nums as $k) {
                     $values[$k] = $this->apcu_fetch((string) $k, $success);
                 }
@@ -642,7 +642,7 @@ protected function apcu_store($key, $var, $ttl = 0)
         if (is_array($key)) {
             $nums = array_filter(array_keys($key), 'is_numeric');
             if ($nums) {
-                $success = [];
+                $success = array();
                 $nums = array_intersect_key($key, array_fill_keys($nums, null));
                 foreach ($nums as $k => $v) {
                     $success[$k] = $this->apcu_store((string) $k, $v, $ttl);

src/Adapters/Couchbase.php

@@ -126,7 +126,7 @@ public function setMulti(array $items, $expire = 0)
         // have to do those piecemeal
         $integers = array_filter(array_keys($items), 'is_int');
         if ($integers) {
-            $success = [];
+            $success = array();
             $integers = array_intersect_key($items, array_fill_keys($integers, null));
             foreach ($integers as $k => $v) {
                 $success[$k] = $this->set((string) $k, $v, $expire);

src/Adapters/Memcached.php

@@ -419,7 +419,7 @@ protected function decode($key)
      */
     protected function setMultiNumericItemsForHHVM(array $items, array $nums, $expire = 0)
     {
-        $success = [];
+        $success = array();
         $nums = array_intersect_key($items, array_fill_keys($nums, null));
         foreach ($nums as $k => $v) {
             $success[$k] = $this->set((string) $k, $v, $expire);