Upgrade travis (#9850)

* upgrade travis

* upgrade travis

.travis.yml

@@ -1,32 +1,22 @@
 language: node_js
 node_js:
   - '6'
-sudo: required
-dist: precise
 services:
   - mongodb
-addons:
-  apt:
-    sources:
-      - ubuntu-toolchain-r-test
-    packages:
-      - g++-4.8
+cache:
+  directories:
+    - 'node_modules'
 before_install:
-  - $CXX --version
   - npm install -g npm@5
-  - if [ $REQUIRES_SERVER ]; then sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10; echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | sudo tee /etc/apt/sources.list.d/mongodb.list; sudo apt-get update; sudo apt-get install mongodb-org-server; fi
-install:
-  - npm install &> npm.install.log || (cat npm.install.log; false)
 before_script:
   - npm run test:build
   - cp config.json.example config.json
-  - sleep 15
+  - sleep 5
 script:
   - npm run $TEST
   - if [ $COVERAGE ]; then ./node_modules/.bin/lcov-result-merger 'coverage/**/*.info' | ./node_modules/coveralls/bin/coveralls.js; fi
 env:
   global:
-    - CXX=g++-4.8
     - DISABLE_REQUEST_LOGGING=true
   matrix:
     - TEST="lint"