Remove dist directory when build release source tar (#115)

diff --git a/Makefile b/Makefile
index b4e7faf..bd19b36 100644
--- a/Makefile
+++ b/Makefile
@@ -117,6 +117,7 @@
 	--exclude .idea \
 	--exclude .DS_Store \
 	--exclude .github \
+	--exclude dist \
 	--exclude $(RELEASE_SRC).tgz \
 	.