Use older version of eslint to stay pre Node.js 1 compliant a little longer

As of writing this, we cannot use the latest version of eslint v2.x
because there's something in there that causes explotions when run
with pre Node.js 1 installed.

package.json

@@ -41,7 +41,7 @@
   },
   "devDependencies": {
     "chai": "^3.4.0",
-    "eslint": "^2.5.1",
+    "eslint": "2.5.1",
     "jshint": "^2.9.5",
     "mocha": "^3.0.2",
     "uglify-js": "^3.4.6",