refactor: change UMD wrapper position

__Refactor:__
Move UMD (Universal Module Definition) wrapper to the top to be always executed.
Fixes an issue that `picturefill` is not defined in Modern Browsers
that have native support for the picture element.
The UMD where never executed because we exit with a `return;`.
```
if ( w.HTMLPictureElement ) {
    w.picturefill = function() { };
    return;
}
```

__Style:__
Trims also some trailing whitespaces which shouldn't be there by definition in the .editorconfig.