url2pkg with github

[coypu%sdf.org@localhost]

Hi,

I had some trouble with some github releases.
I don't have many examples (I always forget to save them), but this is
one:
http://github.com/jbeder/yaml-cpp/releases/tag/release-0.3.0

  url2pkg "https://github.com/jbeder/yaml-cpp/archive/release-0.3.0.tar.gz";
didn't DTRT

How about the following change?
I don't know what is right, I just had to fight github stuff a lot.

In this case, it adds GITHUB_TAG=release-0.3.0

Index: files/url2pkg.pl
===================================================================
RCS file: /cvsroot/pkgsrc/pkgtools/url2pkg/files/url2pkg.pl,v
retrieving revision 1.35
diff -u -r1.35 url2pkg.pl
--- files/url2pkg.pl	7 Jan 2018 11:20:18 -0000	1.35
+++ files/url2pkg.pl	8 Apr 2018 13:08:36 -0000
@@ -382,6 +382,9 @@
 		(($gh_release ne "")
 		? ["GITHUB_RELEASE", $gh_release]
 		: ()),
+		(($gh_tag ne "")
+		? ["GITHUB_TAG", $gh_tag]
+		: ()),
 		(($dist_sufx ne ".tar.gz" && $dist_sufx ne ".gem")
 		? ["EXTRACT_SUFX", $dist_sufx]
 		: ()),