fix(ci): run ci only once on PR

Author: elevatebart

.travis.yml

@@ -1,13 +1,9 @@
 language: node_js
 node_js:
-  - 9
-install:
-  # Use npm 5.7.x since it has introduced `npm ci`
-  - if [[ `npm -v` != 5.7* ]]; then npm install -g npm@'>=5.7.1'; fi
-  - npm ci
+  - 10
 branches:
-  except:
-    - /^v\d+\.\d+\.\d+$/
+  only:
+    - master
 script:
   - npm run test
 stages: