Add support for additional PagesUpdate parameters

[quinqu]

Closes #2261

This change introduces 2 additional parameters provided by the GitHub API to the PagesUpdate type, Public and HTTPSEnforced.

Note: I had to open a new PR because the author email for one of the commits in the first PR did not match the email associated with my CLA.

[codecov]

Codecov Report

Merging #2266 (735ed9f) into master (d4c1caf) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2266   +/-   ##
=======================================
  Coverage   97.81%   97.81%           
=======================================
  Files         114      114           
  Lines       10266    10266           
=======================================
  Hits        10042    10042           
  Misses        156      156           
  Partials       68       68           

Impacted Files	Coverage Δ
github/repos_pages.go	97.11% <ø> (ø)

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[gmlewis]

Thank you, @quinqu !
LGTM.
Merging.