double the max_header_value_length

[InoMurko]

We've seen occurrences of

error] module=Plug.Cowboy function=onresponse/4 ⋅Cowboy returned 400 because it was unable to parse the request headers.
--
  | Feb 20 04:00:17.860 | This may happen because there are no headers, or there are too many headers
  | Feb 20 04:00:17.860 | or the header name or value are too large (such as a large cookie).
  | Feb 20 04:00:17.860 | You can customize those values when configuring your http/https
  | Feb 20 04:00:17.860 | server. The configuration option and default values are shown below:
  | Feb 20 04:00:17.860 | protocol_options: [
  | Feb 20 04:00:17.860 | max_header_name_length: 64,
  | Feb 20 04:00:17.861 | max_header_value_length: 4096,
  | Feb 20 04:00:17.861 | max_headers: 100,
  | Feb 20 04:00:17.861 | max_request_line_length: 8096
  | Feb 20 04:00:17.861 | ]
  | Feb 20 04:00:17.861 | ⋅

added fixes for Statix on our fork bleacherreport/statix#1

[coveralls]

Coverage increased (+0.1%) to 86.317% when pulling 040fe6c on inomurko/increase_header_size into 6e1e593 on master.

[InoMurko]

config get overwritten somehow. needs fixing.