Fix regexify on PHP 5.3

Author: fzaninotto

src/Faker/Provider/Base.php

@@ -434,9 +434,15 @@ public static function regexify($regex = '')
             return static::randomElement(str_split($matches[1]));
         }, $regex);
         // replace \d with number and \w with letter and . with ascii
-        $regex = preg_replace_callback('/\\\w/', 'static::randomLetter', $regex);
-        $regex = preg_replace_callback('/\\\d/', 'static::randomDigit', $regex);
-        $regex = preg_replace_callback('/(?<!\\\)\./', 'static::randomAscii', $regex);
+        $regex = preg_replace_callback('/\\\w/', function() {
+            return static::randomLetter();
+        }, $regex);
+        $regex = preg_replace_callback('/\\\d/', function() {
+            return static::randomDigit();
+        }, $regex);
+        $regex = preg_replace_callback('/(?<!\\\)\./', function() {
+            return static::randomAscii();
+        }, $regex);
         // remove remaining backslashes
         $regex = str_replace('\\', '', $regex);
         // phew