PrettyPrinter\\Standard: fixes nested ternaries output;

[rentalhost]

Fixes #718

That fixes it, but I don't know if it's the best way.

I also had to modify one of the tests, because it is "positively affected" by this commit. The previous expected output would generate the error mentioned in #718.

[nikic]

Thanks for the PR! I've applied a simpler fix in eff72ee. This is just a matter of marking the operator as non-associative.

[rentalhost]

Oh! I almost got it right on my first attempts! I have tried 1 but it brokes other tests. I didn't notice that 0 could be tested as well. Haha!

Thanks a lot for this quick response!