Fix #13274: wrap sourceMap directive in multiline comments

Sizes - compared to 1.9-stable @ 21af3a9213a2ad0f9996f2ef4f2d8ee53a3f45d4
```
    267328         (-)  dist/jquery.js                                         
    138252         (-)  dist/jquery.min.map                                    
     92988         (-)  dist/jquery.min.js                                     
     32963        (-1)  dist/jquery.min.js.gz
```