Set LC_ALL instead of LANG when creating harfbuzz.def

Hopefully fixes Travis faliure?
https://github.com/behdad/harfbuzz/pull/413#issuecomment-278481882
https://travis-ci.org/khaledhosny/harfbuzz/jobs/199785332#L1065

src/Makefile.am

@@ -218,7 +218,7 @@ harfbuzz.def: $(HBHEADERS) $(HBNODISTHEADERS)
 	(cat $^ || echo 'hb_ERROR ()' ) | \
 	$(EGREP) '^hb_.* \(' | \
 	sed -e 's/ (.*//' | \
-	LANG=C sort; \
+	LC_ALL=C sort; \
 	echo LIBRARY libharfbuzz-0.dll; \
 	) >"$@"
 	@ ! grep -q hb_ERROR "$@" \