Update define.amd of dummy define to be an object

**before:**
```JavaScript
function define(){};  define.amd = true;
```

**after**
```JavaScript
function define(){};  define.amd = {};
```

Reasoning: both require.js and `System.amdDefine` expose `.amd` property as an `Object` and that would be expected sometimes for UMD wrappers like that one `lodash` uses:
```JavaScript
if (typeof define == 'function' && typeof define.amd == 'object' && define.amd) {
  // ...
}
```
And "normal/simplified" wrappers wouldn't be affected.
Merge pull request #6 from VasilioRuzanni/patch-1

Update define.amd of dummy define to be an object