RssCrawler doesn't support valid Rss XML

[JeromeGill]

Describe the bug
RssCrawler throws an exception due to not supporting valid RSS
https://github.com/fhamborg/news-please/blob/master/newsplease/single_crawler.py#L202

To Reproduce

dockerfile

FROM python:latest
RUN pip3 install news-please

The following sitelist.hjson

  "base_urls" : [
    {
           "url": "http://feeds.bbci.co.uk/news/world/latin_america/rss.xml",
           "crawler": "RssCrawler"
    }

Expected behavior

RssCrawler loaded and scrape the feed

Log

[newsplease.config:164|INFO] Loading config-file (/root/news-please-repo/config/config.cfg)
[newsplease.config:164|INFO] Loading config-file (/root/news-please-repo/config/config.cfg)
[__main__:200|ERROR] No crawlers (incl. fallbacks) found for url http://feeds.bbci.co.uk/news/world/latin_america/rss.xml.
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/newsplease/single_crawler.py", line 265, in <module>
    SingleCrawler(cfg_file_path=sys.argv[1],
  File "/usr/local/lib/python3.8/site-packages/newsplease/single_crawler.py", line 117, in __init__
    crawler_class = self.get_crawler(self.crawler_name, site["url"])
  File "/usr/local/lib/python3.8/site-packages/newsplease/single_crawler.py", line 202, in get_crawler
    raise RuntimeError("No crawler found. Quit.")
RuntimeError: No crawler found. Quit.
[newsplease.__main__:269|INFO] Graceful stop called manually. Shutting down.

Versions (please complete the following information):

• Python 3.8.0
• news-please Version 1.4.3

[fhamborg]

Could this be related to this PR? #119

[JeromeGill]

That url in this issue is an atom feed, yeah