Fix get-bwc-version for 5.0.0 (#21249)

5.0.0 is at artifacts.elastic.co.

dev-tools/get-bwc-version.py

@@ -67,7 +67,7 @@ def main():
   elif c.version.startswith('0.') or c.version.startswith('1.'):
     url = 'https://download.elasticsearch.org/elasticsearch/elasticsearch/%s' % filename
   else:
-    url = 'http://download.elasticsearch.org/elasticsearch/release/org/elasticsearch/distribution/tar/elasticsearch/%s/%s' % (c.version, filename)
+    url = 'https://artifacts.elastic.co/downloads/elasticsearch/%s' % filename
   print('Downloading %s' % url)
   urllib.request.urlretrieve(url, filename)