dependency retrieval make rule

.travis.yml

@@ -1,3 +1,5 @@
 language: go
 
+install: make deps
+
 script: make

Makefile

@@ -46,3 +46,6 @@ arm6:
 	$(call add-files,$(ARM6))
 	mv oragono $(ARM6)
 	cd $(ARM6) && tar -czvf ../oragono-$(VERS)-arm.tgz *
+
+deps:
+	go get -v -d