Fix codestyle errors

Author: sergiopasra

src/numina/instrument/assembly.py

@@ -7,7 +7,6 @@
 # License-Filename: LICENSE.txt
 #
 
-import collections
 import itertools
 import json
 import pathlib
@@ -56,6 +55,7 @@ def get_default_class(etype):
 _default_class['setup'] = numina.instrument.generic.InstrumentGeneric
 _default_class['properties'] = numina.instrument.generic.InstrumentGeneric
 
+
 @attrs.define
 class ComponentCollection:
     dirname = attrs.field()