.travis.yml fixes for 4.0.x branch (#74)

* Add Node 10 ... (.travis.yml fixes for Node.js 6, 8, and 10) (#53)
* Added Travis CI OSX Image and Install cordova@latest (#59)
* .travis.yml cover deprecated Node.js 4 (4.0.x branch *only*)

Co-authored-by: エリス <erisu@users.noreply.github.com>
Co-authored-by: Christopher J. Brody <chris.brody@gmail.com>
diff --git a/.travis.yml b/.travis.yml
index b151b0b..b23439c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,22 @@
 language: objective-c
+osx_image: xcode9.4
 sudo: false
+
+env:
+  matrix:
+    - TRAVIS_NODE_VERSION: '4'
+    - TRAVIS_NODE_VERSION: '6'
+    - TRAVIS_NODE_VERSION: '8'
+    - TRAVIS_NODE_VERSION: '10'
+
+before_install:
+  - nvm install $TRAVIS_NODE_VERSION
+
 install:
-- npm install
-script: "npm test"
\ No newline at end of file
+  - npm install -g cordova@latest
+  - npm install
+
+script:
+  - node --version
+  - npm --version
+  - npm test