Fix build problem by updating yarn version

Author: SISheogorath

.travis.yml

@@ -4,20 +4,21 @@ cache: yarn
 env:
   global:
     - CXX=g++-4.8
+    - YARN_VERSION=1.3.2
 
 jobs:
   include:
     - env: task=npm-test
       node_js:
         - 6
       before_install:
-        - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.1.0
+        - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version "$YARN_VERSION"
         - export PATH="$HOME/.yarn/bin:$PATH"
     - env: task=npm-test
       node_js:
         - 7
       before_install:
-        - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.1.0
+        - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version "$YARN_VERSION"
         - export PATH="$HOME/.yarn/bin:$PATH"
     - env: task=ShellCheck
       script: