docs(mge/functional): update copy example

GitOrigin-RevId: 2ea102e0ad

imperative/python/megengine/functional/tensor.py

@@ -1050,7 +1050,8 @@ def copy(inp, device=None):
 
     Examples:
 
-        >>> x = Tensor([1, 2, 3], numpy.int32)
+        >>> import numpy as np
+        >>> x = Tensor([1, 2, 3], np.int32)
         Tensor([1 2 3], dtype=int32, device=xpux:0)
 
         >>> F.copy(x, 'cpu1')