Switch to use nodeJsEnv as default jsEnv to build scala.js

By default, scala.js compiler uses `Rhino` as the js environment. But it
usually requires a lot of memory and often lead to OOM. This PR replace
the default to a node.js one that should be much faster and slimer.

.travis.yml

@@ -10,6 +10,11 @@ scala:
 script:
   - scripts/travis-publish.sh
 
+# http://austinpray.com/ops/2015/09/20/change-travis-node-version.html
+install:
+  - 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 $TRAVIS_NODE_VERSION
+  - npm install
+
 notifications:
   webhooks:
     urls:
@@ -21,12 +26,15 @@ env:
   global:
   - secure: Kf44XQFpq2QGe3rn98Dsf5Uz3WXzPDralS54co7sqT5oQGs1mYLYZRYz+I75ZSo5ffZ86H7M+AI9YFofqGwAjBixBbqf1tGkUh3oZp2fN3QfqzazGV3HzC+o41zALG5FL+UBaURev9ChQ5fYeTtFB7YAzejHz4y5E97awk934Rg=
   - secure: QbNAu0jCaKrwjJi7KZtYEBA/pYbTJ91Y1x/eLAJpsamswVOvwnThA/TLYuux+oiZQCiDUpBzP3oxksIrEEUAhl0lMtqRFY3MrcUr+si9NIjX8hmoFwkvZ5o1b7pmLF6Vz3rQeP/EWMLcljLzEwsrRXeK0Ei2E4vFpsg8yz1YXJg=
+  - TRAVIS_NODE_VERSION="4"
 cache:
   directories:
   - $HOME/.sbt/0.13/dependency
   - $HOME/.sbt/boot/scala*
   - $HOME/.sbt/launchers
   - $HOME/.ivy2/cache
+  - $HOME/.nvm
+
 before_cache:
   - du -h -d 1 $HOME/.ivy2/cache
   - du -h -d 2 $HOME/.sbt/

build.sbt

@@ -55,7 +55,11 @@ lazy val commonJsSettings = Seq(
     s"-P:scalajs:mapSourceURI:$a->$g/"
   },
   scalaJSStage in Global := FastOptStage,
-  parallelExecution := false
+  parallelExecution := false,
+  // Using Rhino as jsEnv to build scala.js code can lead to OOM, switch to PhantomJS by default
+  scalaJSUseRhino := false,
+  requiresDOM := false,
+  jsEnv := NodeJSEnv().value
 )
 
 lazy val commonJvmSettings = Seq(