Template Strings as object keys?

Do template strings don't work as object keys?

```
grunt.initConfig({
foo: {thing: "thingo"},
bar: {"<%= foo.thing %>": true}
```

Something like this seems to not be replaced.

Start by reproducing the provided grunt.initConfig example with the template expression used as an object key. Trace how configuration values are processed and determine whether the key should be replaced; done means the example produces the expected substituted key or clearly reports the supported behavior.

Written by the indexing model from the issue text.