yle-dl: install AdobeHDS.php, which is currently a dependency

Yle-dl currently [requires AdobeHDS.php](https://github.com/aajanki/yle-dl#installation) at least for downloading new TV programs. For example,

```
yle-dl http://areena.yle.fi/tv/2247816
```
fails with current yle-dl formula but succeeds after this commit. (Note that areena.yle.fi might be geoblocked.)

I had to make `AdobeHDS.php` executable to keep `brew audit` happy about non-executables, and change the test to allow a nonzero exit value (which `yle-dl --help` has given for some time).
Don't need this `then` but will kill it when I pull.