Bumping nodejs supported engines to ">=0.10.0"

Node 0.8's npm fails to works with "^x.y.z" version specs
(= compatible with x.y.z), which some components already use.

Other than that, amber should work fine wiht node 0.8,
but bumping it anyway.

package.json

@@ -23,7 +23,7 @@
     "url": "git://github.com/amber-smalltalk/amber.git"
   },
   "engines": {
-    "node": ">=0.8.0"
+    "node": ">=0.10.0"
   },
   "scripts": {
     "test": "grunt test"