Makefile should use var defined at top of file

Makefile

@@ -31,19 +31,19 @@ windows:
 	cd $(WIN) && zip -r ../oragono-$(VERS)-windows.zip *
 
 osx:
-	GOOS=darwin GOARCH=amd64 go build oragono.go
+	GOOS=darwin GOARCH=amd64 go build $(SOURCE)
 	$(call add-files,$(OSX))
 	mv oragono $(OSX)
 	cd $(OSX) && tar -czvf ../oragono-$(VERS)-osx.tgz *
 
 linux:
-	GOOS=linux GOARCH=amd64 go build oragono.go
+	GOOS=linux GOARCH=amd64 go build $(SOURCE)
 	$(call add-files,$(LINUX))
 	mv oragono $(LINUX)
 	cd $(LINUX) && tar -czvf ../oragono-$(VERS)-linux.tgz *
 
 arm6:
-	GOARM=6 GOARCH=arm go build oragono.go
+	GOARM=6 GOARCH=arm go build $(SOURCE)
 	$(call add-files,$(ARM6))
 	mv oragono $(ARM6)
 	cd $(ARM6) && tar -czvf ../oragono-$(VERS)-arm.tgz *