Reformat source code with black.

This is the result of:

    $ black --line-length 119 examples templates transformers utils hubconf.py setup.py

There's a lot of fairly long lines in the project. As a consequence, I'm
picking the longest widely accepted line length, 119 characters.

This is also Thomas' preference, because it allows for explicit variable
names, to make the code easier to understand.

utils/link_tester.py

@@ -43,7 +43,7 @@ def scan_code_for_links(source):
     """ Scans the file to find links using a regular expression.
     Returns a list of links.
     """
-    with open(source, 'r') as content:
+    with open(source, "r") as content:
         content = content.read()
         raw_links = re.findall(REGEXP_FIND_S3_LINKS, content)
         links = [prefix + suffix for _, prefix, suffix in raw_links]