update travis config to install node before build

Author: petekanev

.travis.yml

@@ -1,5 +1,6 @@
 env:
   global:
+  - NODE_VERSION=6.11.1
   - NDK_VERSION=r12b
   - DATE=$(date +%Y-%m-%d)
   - PACKAGE_VERSION=next-$DATE-$TRAVIS_BUILD_NUMBER
@@ -37,6 +38,8 @@ before_install:
   - "rm -rf android-ndk-$NDK_VERSION-linux-x86_64.zip"
   - export ANDROID_NDK_HOME=`pwd`/android-ndk-$NDK_VERSION
   - export PATH=${PATH}:${ANDROID_NDK_HOME}
+install:
+  - nvm install $NODE_VERSION
 script:
   - "./gradlew createPackage -i -PpreReleaseVersion=$PACKAGE_VERSION -PgitCommitVersion=$TRAVIS_COMMIT --stacktrace"
   - echo no | android create avd --force -n $EMULATOR_NAME-$EMULATOR_API_LEVEL -t android-$EMULATOR_API_LEVEL --abi $ANDROID_ABI -c 12M