fix flake8 errors, ignore W504

pycodestyle 2.4.0 enforces some new style guidelines

gallery_dl/extractor/seaotterscans.py

@@ -14,7 +14,7 @@ from . import foolslide
 class SeaotterscansChapterExtractor(foolslide.FoolslideChapterExtractor):
     """Extractor for manga-chapters from reader.seaotterscans.com"""
     category = "seaotterscans"
-    pattern = foolslide.chapter_pattern("reader\.seaotterscans\.com")
+    pattern = foolslide.chapter_pattern(r"reader\.seaotterscans\.com")
     test = [("https://reader.seaotterscans.com/read/100_days/en/0/5/", {
         "url": "63d46b8883cc652dfe8bd5be4492160dd31f06a8",
         "keyword": "5349c2fbaa88070e6af600de17a6c4e212243e8e",
@@ -24,7 +24,7 @@ class SeaotterscansChapterExtractor(foolslide.FoolslideChapterExtractor):
 class SeaotterscansMangaExtractor(foolslide.FoolslideMangaExtractor):
     """Extractor for manga from reader.seaotterscans.com"""
     category = "seaotterscans"
-    pattern = foolslide.manga_pattern("reader\.seaotterscans\.com")
+    pattern = foolslide.manga_pattern(r"reader\.seaotterscans\.com")
     test = [("https://reader.seaotterscans.com/series/marry_me/", {
         "url": "fdbacabfa566a6baeb3f01bb46cbda0577bd4bbe",
         "keyword": "61d3388d73df12f64361892b47a9398df4a5947c",

gallery_dl/extractor/worldthree.py

@@ -14,7 +14,7 @@ from . import foolslide
 class WorldthreeChapterExtractor(foolslide.FoolslideChapterExtractor):
     """Extractor for manga-chapters from slide.world-three.org"""
     category = "worldthree"
-    pattern = foolslide.chapter_pattern("(?:www\.)?slide\.world-three\.org")
+    pattern = foolslide.chapter_pattern(r"(?:www\.)?slide\.world-three\.org")
     test = [
         (("http://www.slide.world-three.org"
           "/read/black_bullet/en/2/7/page/1"), {
@@ -33,7 +33,7 @@ class WorldthreeChapterExtractor(foolslide.FoolslideChapterExtractor):
 class WorldthreeMangaExtractor(foolslide.FoolslideMangaExtractor):
     """Extractor for manga from slide.world-three.org"""
     category = "worldthree"
-    pattern = foolslide.manga_pattern("(?:www\.)?slide\.world-three\.org")
+    pattern = foolslide.manga_pattern(r"(?:www\.)?slide\.world-three\.org")
     test = [("http://www.slide.world-three.org/series/black_bullet/", {
         "url": "5743b93512d26e6b540d90a7a5d69208b6d4a738",
         "keyword": "3a24f1088b4d7f3b798a96163f21ca251293a120",

setup.cfg

@@ -1,3 +1,3 @@
 [flake8]
 exclude = gallery_dl/__init__.py,gallery_dl/__main__.py,setup.py,build,scripts,archive
-ignore = E203,E226
+ignore = E203,E226,W504