Build: Fix the regex parsing AMD var-modules (#4389)

Build: Fix the regex parsing AMD var-modules (#4389)

The previous regex caused the final jQuery binary to have syntax errors for
var-modules with names starting with "return". For example, the following module
wouldn't work when the file is named `returnTrue.js`:

```js
define( function() {
	"use strict";
	return function returnTrue() {
		return true;
	};
} );
```

Closes gh-4389

(cherry picked from commit 9ec09c3b4aa5182c2a8b8f51afb861b685a4003c)