use iojs 1.5.x, see iojs/io.js#1103 + iojs/io.js#1075

.travis.yml

@@ -1,6 +1,6 @@
 language: node_js
 node_js:
-  - "iojs-v1.4.1"
+  - "iojs-v1.5.1"
 before_script:
   - cp "lib/config.example.js" "lib/config.js"
 before_install:

package.json

@@ -26,7 +26,7 @@
     "test": "istanbul cover ./node_modules/mocha/bin/_mocha --report lcovonly -- -R spec && cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js && rm -rf ./coverage"
   },
   "engines": {
-    "iojs": "1.4.x"
+    "iojs": "1.5.x"
   },
   "dependencies": {
     "canvas": "crafatar/node-canvas",