feat(ci): update node version

Author: rande

.travis.yml

@@ -9,7 +9,7 @@ cache:
 install:
     # from http://austinpray.com/ops/2015/09/20/change-travis-node-version.html
     - make install-backend
-    - rm -rf ~/.nvm && git clone https://github.com/creationix/nvm.git ~/.nvm && (cd ~/.nvm && git checkout `git describe --abbrev=0 --tags`) && source ~/.nvm/nvm.sh && nvm install 4.4.5
+    - rm -rf ~/.nvm && git clone https://github.com/creationix/nvm.git ~/.nvm && (cd ~/.nvm && git checkout `git describe --abbrev=0 --tags`) && source ~/.nvm/nvm.sh && nvm install 8.12.0
     - npm -g install yarn
     - make install-frontend