install current yarn version on travis build

Author: appinteractive

.travis.yml

@@ -10,10 +10,8 @@ cache:
 
 # install current version of yarn
 before_install:
-  - curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
-  - echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
-  - sudo apt-get update && sudo apt-get install yarn
-  - export PATH=$HOME/.yarn/bin:$PATH
+  - curl -o- -L https://yarnpkg.com/install.sh | bash
+  - export PATH="$HOME/.yarn/bin:$PATH"
 
 jobs:
   include: