fix iojs version in .travis.yml (again)

.travis.yml

@@ -1,6 +1,6 @@
 language: node_js
 node_js:
-  - "iojs-v1.8.0"
+  - "iojs-v1.8"
 before_install:
   - sudo apt-get install libcairo2-dev libjpeg8-dev libpango1.0-dev libgif-dev build-essential g++
 script: