add yarn (#29)

gengjiawen · web-flow · commit e774f1fe734f · 2019-10-11T15:56:15.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -15,6 +15,7 @@ cache:
   - $HOME/.cache/electron-builder
 
 before_script:
+  - npm i -g yarn
   - npx envinfo
 
 script:
