Update yarn version

Author: Ace Nassri

circle.yml

@@ -20,7 +20,7 @@ machine:
   node:
     version: 6.9.1
   environment:
-    YARN_VERSION: 0.19.1
+    YARN_VERSION: 0.22.0
     PATH: "${PATH}:${HOME}/.yarn/bin:${HOME}/${CIRCLE_PROJECT_REPONAME}/node_modules/.bin"
   services:
     - redis