Switch to Python 3

https://bugzilla.redhat.com/show_bug.cgi?id=1509660

gtk-doc.spec

@@ -1,5 +1,7 @@
 %global debug_package %{nil}
 
+%global __python %{__python3}
+
 Name: gtk-doc
 Version: 1.28
 Release: 1%{?dist}
@@ -13,15 +15,15 @@ BuildRequires: dblatex
 BuildRequires: docbook-utils
 BuildRequires: /usr/bin/xsltproc
 BuildRequires: docbook-style-xsl
-BuildRequires: python2-devel
-BuildRequires: python2-six
 BuildRequires: gettext
+BuildRequires: python3-devel
+BuildRequires: python3-six
 BuildRequires: source-highlight
 BuildRequires: yelp-tools
 
 # Following are not automatically installed
 Requires: docbook-utils /usr/bin/xsltproc docbook-style-xsl
-Requires: python2-six
+Requires: python3-six
 Requires: source-highlight
 
 %description
@@ -36,6 +38,7 @@ and GNOME.
 mv doc/README doc/README.docs
 
 %build
+export PYTHON=%{__python3}
 %configure
 make %{?_smp_mflags}
 
@@ -60,6 +63,7 @@ make check || make check
 %changelog
 * Sat Mar 24 2018 Kalev Lember <klember@redhat.com> - 1.28-1
 - Update to 1.28
+- Switch to Python 3 (#1509660)
 
 * Wed Feb 07 2018 Fedora Release Engineering <releng@fedoraproject.org> - 1.27-2
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_28_Mass_Rebuild