[5.5] Fixed json responses

[GrahamCampbell]

The current code breaks the exception handler returning json responses: https://github.com/laravel/framework/blob/5.4/src/Illuminate/Foundation/Exceptions/Handler.php#L223.

Here are the headers before and after:

Clearly this is wrong. The laravel response class should never be removing content types provided by the user!

[taylorotwell]

We would need a description.

[GrahamCampbell]

We would need a description.

Ha, see slack. I'll copy it over. Give me a min. :P Also, the test I've added shows what this fixes.

[GrahamCampbell]

Description added. Was jet lagged af when I PRed this (still am). :D

[taylorotwell]

I feel like this had to there for a reason and we are probably breaking something by removing it. I would like to find out what that is. /cc @themsaid

[m1guelpf]

@taylorotwell Maybe you should start on the PR this was added... #18314

[taylorotwell]

@lucasmichot any comment on this?

[GrahamCampbell]

I feel like this had to there for a reason and we are probably breaking something by removing it.

The other PR didn't provide a real reason?

[GrahamCampbell]

The reason given was:

and yet it only works after this PR is merged, because we can't pass real json anymore.

[GrahamCampbell]

I think the original PR was stupid anyway, because it forces everything to json, and doesn't let you opt-out.