Update app.py

app.py

@@ -30,7 +30,7 @@ def splitIsnad(dataframe):
     
 def network_visualizer(city, year):
     edge_15 = splitIsnad(subsetEdges(city, year)).sample(300)
-    nt = Network()
+    net = Network()
     for _, row in edge_15.iterrows():
         source = row['Teacher']
         target = row['Student']