fix pylint complaint

Author: jcurtis2

tests/test_gas_state.py

@@ -60,7 +60,7 @@ def test_get_item_out_of_range(idx):
     def test_get_item_valid():
         # arrange
         sut = ppmc.GasState(GAS_DATA_MINIMAL)
-        sut.__setitem__(0,44)
+        sut[0] = 44
         # act
         value = sut[0]