python/demos/demo_filterbank.py: fix header

diff --git a/python/demos/demo_filterbank.py b/python/demos/demo_filterbank.py
index 7080864..1620a03 100755 (executable)
--- a/python/demos/demo_filterbank.py
+++ b/python/demos/demo_filterbank.py
@@ -1,4 +1,4 @@
-#! /usr/bin/python
+#! /usr/bin/env python
 
 from aubio import filterbank, fvec
 from pylab import loglog, show, subplot, xlim, ylim, xlabel, ylabel, title