Fix on test 'cpp_classes'

tests/run/cpp_classes.pyx

@@ -19,6 +19,7 @@ cdef extern from "shapes.h" namespace shapes:
     cdef cppclass Rectangle(Shape):
         int width
         int height
+        Rectangle()
         Rectangle(int, int)
     
     cdef cppclass Square(Rectangle):

tests/run/shapes.h

@@ -17,6 +17,7 @@ namespace shapes {
     class Rectangle : public Shape
     {
     public:
+    	Rectangle() { }
         Rectangle(int width, int height) 
         {
             this->width = width;