run flake8 on all .py files

gallery_dl/__init__.py

@@ -238,7 +238,8 @@ def main():
                             if sys.stdin:
                                 urls += parse_inputfile(sys.stdin, log)
                             else:
-                                log.warning("input file: stdin is not readable")
+                                log.warning(
+                                    "input file: stdin is not readable")
                         else:
                             with open(inputfile, encoding="utf-8") as file:
                                 urls += parse_inputfile(file, log)

setup.cfg

@@ -1,5 +1,5 @@
 [flake8]
-exclude = gallery_dl/__init__.py,gallery_dl/__main__.py,setup.py,build,scripts,archive
+exclude = build,scripts,archive
 ignore = E203,E226,W504
 per-file-ignores =
     gallery_dl/extractor/500px.py: E501