switch from node 0.12 to iojs 1.2, closes #89

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": {
-    "node": "0.12.x"
+    "iojs": "1.2.x"
   },
   "dependencies": {
     "canvas": "crafatar/node-canvas",