fix xml.instruct bug when arguments are used

lib/asbestos.rb

@@ -46,7 +46,7 @@ def target!
       @target
     end
 
-    def instruct!
+    def instruct!(*args)
     end
 
     def tag!(sym, *args, &block)

spec/asbestos_spec.rb

@@ -54,6 +54,11 @@ def to_json
     to_json.should == '{}'
   end
 
+  it "should ignore instruct when used with attributes" do
+    @json.instruct! :xml, :version => "1.0" 
+    to_json.should == '{}'
+  end
+
   it "should support ignores" do
     @json = described_class.new(:ignore => ['foo'])
     @json.foo do