Add UPSTREAM_TAG to elixir_wrapper make file

package.mk.diff

--- a/package.mk
+++ b/package.mk
@@ -3,6 +3,7 @@ DO_NOT_GENERATE_APP_FILE:=true

 UPSTREAM_GIT:=git://github.com/elixir-lang/elixir.git
 UPSTREAM_REVISION:=master
+UPSTREAM_TAG:=v0.12.0
 RETAIN_ORIGINAL_VERSION:=true

 ORIGINAL_APP_FILE=$(CLONE_DIR)/src/$(APP_NAME).app.src
@@ -19,5 +20,5 @@ endef
 define construct_app_commands
        cp -r $(CLONE_DIR)/lib/elixir/ebin $(APP_DIR)
        cp -r $(CLONE_DIR)/lib/elixir/include $(APP_DIR)
-       cp -r $(CLONE_DIR)/lib/elixir/priv $(APP_DIR)
+       cp -r $(CLONE_DIR)/lib/elixir/priv $(APP_DIR) 2>/dev/null || :
 endef