update travis.yml

Author: AmazingMoon

.travis.yml

@@ -4,6 +4,9 @@ services:
 - docker
 node_js:
 - 11.12
+branches:
+  only: 
+    - master
 before_install:
 - openssl aes-256-cbc -K $encrypted_213c7ad97f24_key -iv $encrypted_213c7ad97f24_iv
   -in id_rsa.enc -out ~/.ssh/id_rsa -d