[scikit-learn] CI permissions

[Andreas Mueller]

Hey all.
So I think I messed with the CI a bit too much yesterday.
After looking into the organization permissions a bit more, I saw that 
any app that is authorized on github by any of the devs
will automatically be authorized for the organization.
That seems pretty bad.

So I change that default to each app needing to be authorized explicitly 
for the organization.
Clearly I wasn't thinking, because that broke CI.
I gave permissions back to the CI services, but they are not all linked 
to my account.
Olivier, can you check for coveralls and circleci? I think you have 
these accounts.
Appveyor and travis are working again.

Sorry for the inconvenience,
Andy