fix _get_extra_repr

Author: naspert

pygsp/graphs/nngraphs/nngraph.py

@@ -345,7 +345,7 @@ def __init__(self, Xin, NNtype='knn', backend='scipy-ckdtree', center=True,
 
     def _get_extra_repr(self):
         return {'NNtype': self.NNtype,
-                'use_flann': self.use_flann,
+                'backend': self.backend,
                 'center': self.center,
                 'rescale': self.rescale,
                 'k': self.k,