community/gtkspell3: add missing gtk-doc makedepends

> Can't exec "gtkdocize": No such file or directory at
> /usr/share/autoconf/Autom4te/FileUtils.pm line 293.

community/gtkspell3/APKBUILD

@@ -8,7 +8,7 @@ url="http://gtkspell.sourceforge.net/"
 arch="all"
 license="GPL-2.0-or-later"
 makedepends="enchant2-dev gtk+3.0-dev vala gobject-introspection-dev
-	automake autoconf libtool intltool"
+	automake autoconf libtool intltool gtk-doc"
 options="!check" # no tests
 subpackages="$pkgname-static $pkgname-dev $pkgname-doc $pkgname-lang"
 source="https://downloads.sourceforge.net/gtkspell/gtkspell3-$pkgver.tar.xz"