Fix export courses

courses/import_export/views.py

@@ -71,7 +71,7 @@ class ExportCourseView(APIView):
         course_material = course_serializer.data.get('course_material')
         if course_material:
             for course_material_file in course_material['files']:
-                course_material_file_path = urllib.unquote(course_material_file['file'])
+                course_material_file_path = urllib.parse.unquote(course_material_file['file'])
                 self.add_files_to_export(course_tar_file, course_material_file_path)
 
         # If there are any activities of type 'image', its files must be saved here
@@ -80,7 +80,7 @@ class ExportCourseView(APIView):
                 for activity in unit.activities.all():
                     if activity.type == 'image':  # check if the current activity is of 'image' type
                             try:
-                                activity_image_file_path = urllib.unquote(activity.image.url)
+                                activity_image_file_path = urllib.parse.unquote(activity.image.url)
                                 self.add_files_to_export(course_tar_file, activity_image_file_path)
                             except ValueError:
                                 # There is no image file associated with the activity yet