Update integrations/server/test_covidcast_endpoints.py

- list comprehension readability

Co-authored-by: Katie Mazaitis <krivard@cs.cmu.edu>

Author: dshemetov

integrations/server/test_covidcast_endpoints.py

@@ -50,7 +50,10 @@ def _fetch(self, endpoint="/", is_compatibility=False, **params):
         return response.json()
 
     def _diff_rows(self, rows: Sequence[float]):
-        return [float(x - y) if x is not None and y is not None else None for x, y in zip(rows[1:], rows[:-1])]
+        return [
+            float(x - y) if x is not None and y is not None else None
+            for x, y in zip(rows[1:], rows[:-1])
+        ]
 
     def _smooth_rows(self, rows: Sequence[float]):
         return [sum(e)/len(e) if None not in e else None for e in windowed(rows, 7)]