Add missing pkgconfig(glib-2.0) dep

Traceback when building other modules:

Traceback (most recent call last):
  File "/usr/bin/gtkdoc-rebase", line 56, in <module>
    sys.exit(rebase.run(options))
  File "/usr/share/gtk-doc/python/gtkdoc/rebase.py", line 66, in run
    dir = common.GetModuleDocDir('glib-2.0')
  File "/usr/share/gtk-doc/python/gtkdoc/common.py", line 104, in GetModuleDocDir
    path = subprocess.check_output([config.pkg_config, '--variable=prefix', module_name], universal_newlines=True)
  File "/usr/lib64/python2.7/subprocess.py", line 219, in check_output
    raise CalledProcessError(retcode, cmd, output=output)
subprocess.CalledProcessError: Command '['/usr/bin/x86_64-redhat-linux-gnu-pkg-config', '--variable=prefix', 'glib-2.0']' returned non-zero exit status 1

gtk-doc.spec

@@ -2,7 +2,7 @@
 
 Name: gtk-doc
 Version: 1.26
-Release: 1%{?dist}
+Release: 2%{?dist}
 Summary: API documentation generation tool for GTK+ and GNOME
 
 License: GPLv2+ and GFDL
@@ -24,6 +24,7 @@ BuildRequires: yelp-tools
 
 # Following are not automatically installed
 Requires: docbook-utils /usr/bin/xsltproc docbook-style-xsl
+Requires: pkgconfig(glib-2.0)
 Requires: python2-six
 Requires: source-highlight
 
@@ -61,6 +62,9 @@ make check || make check
 %{_libdir}/cmake/
 
 %changelog
+* Fri Oct 06 2017 Kalev Lember <klember@redhat.com> - 1.26-2
+- Add missing pkgconfig(glib-2.0) dep
+
 * Tue Aug 15 2017 Kalev Lember <klember@redhat.com> - 1.26-1
 - Update to 1.26
 - Don't own /usr/share/gtk-doc/html/ -- packages that drop files in there need