drop support for node 0.6 in travis and package.json

.travis.yml

@@ -1,5 +1,4 @@
 language: node_js
 node_js:
-  - 0.6
   - 0.8
   - 0.10

package.json

@@ -26,6 +26,6 @@
     "test": "vows --spec"
   },
   "engines": {
-    "node": ">= 0.6.5"
+    "node": ">= 0.8.0"
   }
 }