travis: Switch to Node.js 0.10

This repository is mainly about client-side javascript, the version
of Node.js used for the build scripts doesn't really matter.

One of the dependencies in package.json uses the '^x.x' syntax in
its sub-dependencies and isn't supporteed on Node.js 0.8, which
is why the Travis CI build is currently erroring on the install step.

package.json

@@ -43,7 +43,7 @@
     "url" : "http://github.com/wikimedia/jquery.uls/issues"
   },
   "engine": {
-    "node": ">=0.6.x"
+    "node": ">=0.10.x"
   },
   "licenses": [
     {