Bump nodejs version to 6+ (#4272)

* let travis build against 3.x

* Cleanup dependencies and bump min version to current LTS

* Makes npm-git push all branches to -preview

* restores releases

* Bumps mime to 2.0.3 (requires node 6+)

* Bumps express to latest version

* Fixes linting issue after upgrade

* Use travis-branch for partial releases

.travis.yml

@@ -25,13 +25,13 @@ stage: test
 env:
   global:
   - COVERAGE_OPTION='./node_modules/.bin/nyc'
-  - NODE_VERSION=6.10 
+  - NODE_VERSION=6.11.4
   matrix:
   - MONGODB_VERSION=3.2.13
   - MONGODB_VERSION=3.4.4
   - PARSE_SERVER_TEST_DB=postgres
   - PARSE_SERVER_TEST_CACHE=redis
-  - NODE_VERSION=8.5
+  - NODE_VERSION=8.7
 before_install:
 - nvm install $NODE_VERSION
 - nvm use $NODE_VERSION
@@ -48,7 +48,7 @@ jobs:
   include:
     # release on github latest branch
     - stage: release
-      node_js: '4.6'
+      node_js: '6.11.4'
       env: 
       before_script: skip
       after_script: skip
@@ -58,7 +58,9 @@ jobs:
           skip_cleanup: true
           script: ./resources/npm-git.sh
           on:
-           branch: master
+           branch:
+            - master
+            - 3.x
         - provider: npm
           skip_cleanup: true
           email: