Log Message:
ruby-pkg-config: update to 1.3.6.

Upstream changes (from NEWS):

== 1.3.6 - 2019-03-09

=== Improvements

  * Added support for Homebrew environment without pkg-config formula.

== 1.3.5 - 2019-03-08

=== Fixes

  * Fixed MSYS2 detection installed at non standard folder.
    [GitHub:ruby-gnome2/ruby-gnome2#1271][Reported by Simon Arnaud]

=== Thanks

* Simon Arnaud