change dependency to git url until PR merged upstream, test travis against 0.10,0.12

.travis.yml

@@ -2,4 +2,5 @@ language: node_js
 script: "npm run unit"
 node_js:
   - "0.10"
+  - "0.12"
 sudo: false

package.json

@@ -34,7 +34,7 @@
   },
   "dependencies": {
     "async": "^0.9.0",
-    "cluster2": "^0.4.26",
+    "cluster2": "git://github.com/missinglink/cluster2.git#node_zero_twelve",
     "express": "^4.8.8",
     "geojson": "^0.2.1",
     "geojson-extent": "^0.3.1",