use latest node in travis

.travis.yml

@@ -21,8 +21,8 @@ before_install:
   - git submodule update --init --recursive
   - git clone https://github.com/creationix/nvm.git ./.nvm
   - source ./.nvm/nvm.sh
-  - nvm install 0.12
-  - nvm use 0.12
+  - nvm install node
+  - nvm use node
   - npm install -g npm@2
   - npm config set python `which python`
   - npm install -g gulp