Fix: only deploy when tag is present

.travis.yml

@@ -25,8 +25,10 @@ after_script:
 # Releases deployed on GitHub
 deploy:
   provider: releases
+  skip_cleanup: true
   api_key:
     secure: feyz5YmzYj6g6ZJKAv7u3pp9j9OY6oL4Pcx8mkha25BT1kEIu7lzvkZu4mJAIDjCxJjEkce3fNGXhRICqoMhRy/FK5dUUTpmP3KoMLNNJboO+MhDqjPEb6OYyafikSWnm0BszPL38FzSYMdmvNZ6WirOyVfrdzVPgU6MG0D99w8=
   file: ucoin.tar.gz
   on:
     repo: ucoin-io/ucoin
+    tags: true