update dependenis and fix flake8 error

src/common/email.py

@@ -14,7 +14,7 @@ def read_email(name):
 def registration(user):
     subject = "Kszképzés regisztráció"
     message = read_email('registration.txt')
-    message = str.format(message %{'name': user.get_full_name()})
+    message = str.format(message % {'name': user.get_full_name()})
     send_mail(subject, message, sender_email, [user.email, ])
 
 
@@ -47,5 +47,5 @@ def homework_corrected(user, title, accepted):
     else:
         status = 'Hibás'
     message = read_email('homework_corrected.txt')
-    message = str.format(message % {'name': user.get_full_name(), 'link': link, 'status': status, 'title': title })
+    message = str.format(message % {'name': user.get_full_name(), 'link': link, 'status': status, 'title': title})
     send_mail(subject, message, sender_email, [user.email, ])

src/homework/serializers.py

@@ -64,7 +64,7 @@ class SolutionSerializer(serializers.ModelSerializer):
         return value
 
     def update(self, instance, validated_data):
-        if instance.corrected == False and validated_data.get('corrected', instance.corrected) == True:
+        if instance.corrected is not True and validated_data.get('corrected', instance.corrected) is True:
             email.homework_corrected(
                 instance.created_by.user,
                 instance.task.title,
@@ -76,4 +76,3 @@ class SolutionSerializer(serializers.ModelSerializer):
         profile = CurrentUserMiddleware.get_current_user_profile()
         models.Solution.objects.filter(created_by=profile, task=validated_data['task']).delete()
         return super().create(validated_data)
-