pull-license-list: Update to Python 3.6

Which adds support for parsing JSON directly from bytes without first
decoding to a string [1,2].  This allows interacting with
RFC-compliant servers, because RFC 7159 does not define a charset
parameter in its application/json registration [3].

Reported by Eric Searcy [4].

[1]: https://docs.python.org/3/whatsnew/3.6.html#json
[2]: https://bugs.python.org/issue17909
[3]: https://tools.ietf.org/html/rfc7159#page-11
[4]: spdx#10 (comment)

bin/pull-license-list.py

@@ -12,19 +12,22 @@
 import json
 import os.path
 import re
+import sys
 import urllib.request
 
 
+if sys.version_info < (3, 6):
+    raise RuntimeError('this script requires Python 3.6+')
+
+
 VERSION_REGEXP = re.compile(
     pattern='(.* SPDX License List, v)([^ ]*)( which was released )([^.]*)(\..*)',
     flags=re.DOTALL)
 
 
 def get_json(url):
     with urllib.request.urlopen(url=url) as response:
-        charset = response.headers.get_content_charset('UTF-8')
-        reader = codecs.getreader(charset)
-        return json.load(reader(response))
+        return json.load(body)
 
 
 def format_table(headers, rows):