typo fix

observation_sim/mock_objects/SpecDisperser/SpecDisperser.py

@@ -336,7 +336,7 @@ class SpecDisperser(object):
         orders = {"A": "1st", "B": "0st", "C": "2st", "D": "-1st", "E": "-2st"}
         sens_file_name = conffile[0:-5] + \
             "_sensitivity_" + orders[beam] + ".fits"
-        if os.path.exists(sens_file_name) if False:
+        if os.path.exists(sens_file_name) is False:
             senstivity_out = Table(
                 array([w, sens]).T, names=("WAVELENGTH", "SENSITIVITY"))
             senstivity_out.write(sens_file_name, format="fits")