Fixing an issue where env is out of scope when baseTag is called

I've setup a broken blueprint example here: https://github.com/lpetre/ember-cli-broken

You can see I set the baseURL depending on the environment here: https://github.com/lpetre/ember-cli-broken/blob/master/config/environment.js#L3

This is the bug:
```
$ ./node_modules/.bin/ember build && cat dist/index.html | grep base
version: 0.0.27
Built project successfully. Stored in "dist/".
    <base href="/undefined" />
      window.ENV = {"baseURL":"/development","locationType":"auto","FEATURES":{},"APP":{"LOG_RESOLVER":true,"LOG_ACTIVE_GENERATION":true,"LOG_MODULE_RESOLVER":true,"LOG_VIEW_LOOKUPS":true},"LOG_MODULE_RESOLVER":true};
```