Support php's array callable format for macro's.

This allows you to define methods like this as well: Str::macro('name', [$this, 'method']);

src/Macro.php

@@ -10,14 +10,19 @@ class Macro extends Method
     /**
      * Macro constructor.
      *
-     * @param \ReflectionFunction $method
+     * @param \ReflectionFunctionAbstract $method
      * @param string              $alias
      * @param \ReflectionClass    $class
      * @param null                $methodName
      * @param array               $interfaces
      */
-    public function __construct(\ReflectionFunction $method, $alias, $class, $methodName = null, $interfaces = array())
-    {
+    public function __construct(
+        \ReflectionFunctionAbstract $method,
+        $alias,
+        $class,
+        $methodName = null,
+        $interfaces = array()
+    ) {
         $this->method = $method;
         $this->interfaces = $interfaces;
         $this->name = $methodName ?: $method->name;