Fix alembic file template

Author: wu-clan

backend/alembic.ini

@@ -7,7 +7,7 @@ script_location = alembic
 
 # template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
 # Uncomment the line below if you want the files to be prepended with date and time
-file_template = %%(year)d-%%(month).2d-%%(day).2d-%%(hour).2d:%%(minute).2d:%%(second).2d-%%(rev)s_%%(slug)s
+file_template = %%(year)d-%%(month).2d-%%(day).2d-%%(hour).2d_%%(minute).2d_%%(second).2d-%%(rev)s_%%(slug)s
 
 # sys.path path, will be prepended to sys.path if present.
 # defaults to the current working directory.