Update travis configuration to test on nodejs v9 and v10 (#277)

* Update to node 10 in .travis.yml

* Add checks on nodejs v9

* Add nodejs 9/10 to appveyor

Author: aivus

.travis.yml

@@ -6,6 +6,8 @@ node_js:
   - '6'
   - '7'
   - '8'
+  - '9'
+  - '10'
 after_success:
   - travis_retry codeclimate-test-reporter < coverage/lcov.info
   - travis_retry coveralls < coverage/lcov.info

appveyor.yml

@@ -5,6 +5,8 @@ environment:
   - nodejs_version: "6"
   - nodejs_version: "7"
   - nodejs_version: "8"
+  - nodejs_version: "9"
+  - nodejs_version: "10"
 
 install:
   - ps: Install-Product node $env:nodejs_version