(fix) Fix PEP8 typo

Author: kryzar

src/sage/rings/function_field/drinfeld_modules/drinfeld_module.py

@@ -589,7 +589,7 @@ def __classcall_private__(cls, function_ring, gen, name='t'):
             base_morphism = Hom(function_ring, base_field_noext)(gen[0])
             base_field = base_field_noext.over(base_morphism)
 
-        # This test is also done in the category. We put it here also 
+        # This test is also done in the category. We put it here also
         # to have a friendlier error message
         if not base_field.is_field():
             raise ValueError('generator coefficients must live in a field')