gnunet: fix build

a missing empty file caused the build to break

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

net/gnunet/Makefile

@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=gnunet
-PKG_SOURCE_VERSION:=d7570f9f93da1c15658b0eff5897d301f7bbedd3
+PKG_SOURCE_VERSION:=a4295da3df82817ff2fe1fa547374a96a2e0280b
 PKG_VERSION:=0.10.2-git-20170111-$(PKG_SOURCE_VERSION)
 PKG_RELEASE:=1