bump req libxcb

[coypu%sdf.org@localhost]

libXest is failing on netbsd-6-0:

configure: error: Package requirements (xproto >= 7.0.13 x11 >= 1.6
xextproto >= 7.1.99) were not met:

Package dependency requirement 'xcb >= 1.11.1' could not be satisfied.
Package 'xcb' has version '1.7', required version is '>= 1.11.1'

I've tested in a netbsd 6.0.6 chroot. It builds with this change.

OK to commit?

? libXext/work
? qt5-qtbase/work
? xcb-util/work
Index: libxcb/buildlink3.mk
===================================================================
RCS file: /cvsroot/pkgsrc/x11/libxcb/buildlink3.mk,v
retrieving revision 1.4
diff -u -r1.4 buildlink3.mk
--- libxcb/buildlink3.mk	29 May 2014 00:39:47 -0000	1.4
+++ libxcb/buildlink3.mk	28 Mar 2017 19:25:00 -0000
@@ -5,8 +5,8 @@
 .if !defined(LIBXCB_BUILDLINK3_MK)
 LIBXCB_BUILDLINK3_MK:=
 
-BUILDLINK_API_DEPENDS.libxcb+=	libxcb>=1.6
-BUILDLINK_ABI_DEPENDS.libxcb+=	libxcb>=1.6
+BUILDLINK_API_DEPENDS.libxcb+=	libxcb>=1.11.1
+BUILDLINK_ABI_DEPENDS.libxcb+=	libxcb>=1.11.1
 BUILDLINK_PKGSRCDIR.libxcb?=	../../x11/libxcb
 
 .include "../../mk/bsd.fast.prefs.mk"