Use latest stable yarn to make resolutions work

Fix jestjs/jest#8050

TypeError: Cannot assign to read only property 'Symbol(Symbol.toStringTag)' of object '#<process>'

https://travis-ci.org/msand/react-native-svg-e2e/jobs/502745672

.travis.yml

@@ -79,6 +79,8 @@ jobs:
         - cd -
       install:
         - nvm install node
+        - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.13.0
+        - export PATH=$HOME/.yarn/bin:$PATH
         - yarn global add react-native-cli
         - yarn global add detox-cli
         - yarn add detox@msand/detox-patch-build#07f01ce