gtk-doc: move back to EAPI=6

The downgrade to EAPI=5 missed the eapply statement.
Now that we support EAPI=6, move back up.

BUG=chromium:1026092
TEST=`sudo emerge gtk-doc` works

Change-Id: I97418397f750e7b94c08bf004ccc6f9cfbf46e57
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/1923013
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/dev-util/gtk-doc/gtk-doc-1.25-r1.ebuild b/dev-util/gtk-doc/gtk-doc-1.25-r1.ebuild
index d1bb5b9..d5df5cf 100644
--- a/dev-util/gtk-doc/gtk-doc-1.25-r1.ebuild
+++ b/dev-util/gtk-doc/gtk-doc-1.25-r1.ebuild
@@ -1,7 +1,7 @@
 # Copyright 1999-2018 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
-EAPI=5
+EAPI=6
 PYTHON_COMPAT=( python2_7 )
 
 inherit eutils elisp-common gnome2 python-single-r1 readme.gentoo-r1