Make xref depend on compile
diff --git a/tools.mk b/tools.mk
index 15a55f7..8e0e1b9 100644
--- a/tools.mk
+++ b/tools.mk
@@ -4,7 +4,7 @@
 docs:
 	./rebar doc skip_deps=true
 
-xref:
+xref: compile
 	./rebar xref skip_deps=true
 
 PLT ?= $(HOME)/.riak_combo_dialyzer_plt