Remove inital yarn install

Author: HazAT

.travis.yml

@@ -19,8 +19,6 @@ matrix:
         - echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
         - travis_retry sudo apt-get update -qq
         - travis_retry sudo apt-get install -y -qq yarn
-      install:
-        - yarn
       android:
         components:
           - build-tools-23.0.1