travis: try to fix npm problems with node 0.8

... by installing latest npm by hand

.travis.yml

@@ -1,7 +1,9 @@
 language: node_js
 node_js:
-#  - "0.8" # has npm problems
+  - "0.8"
   - "0.10"
+before_install:
+  - npm -g install npm@1.x.x
 install:
   - npm install -g grunt-cli
   - npm install

package.json

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