Add Content-Type response header for JSON responses

[dlichtenberger]

Fixes #88

[dlichtenberger]

So some updater tests fail, but the error message seems to indicate that this has nothing to do with this PR:

Exception: Updates between multiple major versions and downgrades are unsupported.

[MorrisJobke]

So some updater tests fail, but the error message seems to indicate that this has nothing to do with this PR:

Exception: Updates between multiple major versions and downgrades are unsupported.

Yep. Seems that we linked the wrong URL and those now ship a new version of Nextcloud to which the upgrade is not supported. Sadly currently I have limited time to look into this. I will do so later.

[PVince81]

@dlichtenberger I know it's old. If you'd still like to get this in please rebase or recreate.

I've just fixed the test problems on master so your PR should be green on the next run.

[solracsf]

/rebase

[come-nc]

I think DCO is not a big deal on a one-line change like this?
And the test failure is not related.
Can someone with power force merge this?

[joshtrichards]

I set the DCO test to pass and updated to latest master. All tests passing.