fix dtype for pluggable object

Author: tomvanmele

src/compas/geometry/curves/nurbs.py

@@ -122,6 +122,11 @@ def __str__(self):
     # Data
     # ==============================================================================
 
+    @property
+    def dtype(self):
+        """str : The type of the object in the form of a '2-level' import and a class name."""
+        return 'compas.geometry/NurbsCurve'
+
     @property
     def data(self):
         return {