build: support Node.js 5.x

.travis.yml

@@ -7,6 +7,7 @@ node_js:
   - "2.5"
   - "3.3"
   - "4.2"
+  - "5.3"
 sudo: false
 before_install:
   # Setup Node.js version-specific dependencies

appveyor.yml

@@ -7,6 +7,7 @@ environment:
     - nodejs_version: "2.5"
     - nodejs_version: "3.3"
     - nodejs_version: "4.2"
+    - nodejs_version: "5.3"
 install:
   - ps: Install-Product node $env:nodejs_version
   - if "%nodejs_version%" equ "0.8" npm rm --save-dev istanbul