Updated node versions matrix and added SKIP_DTRACE=1 env var

Author: Srokap

.travis.yml

@@ -4,13 +4,16 @@ os:
   - linux
   - osx
 
+env:
+ - SKIP_DTRACE=1
+
 node_js:
   - '0.10'
   - '0.12'
   - '4'
   - '5'
+  - '6'
   - 'node'
-  - 'iojs'
 
 # Gives us faster boot time, see https://docs.travis-ci.com/user/ci-environment/
 sudo: false