gocritic enabled by default check list

[lopezator]

I don't know exactly what criteria is being followed to enable or not by default a check inside gocritic.

Since latest gocritic update on: #329 a lot new stable checks were added to gocritic.

Maybe it makes sense to keep this:

https://github.com/golangci/golangci-lint/blob/master/pkg/config/config.go#L260

In sync witn this:

https://github.com/go-critic/go-critic/blob/master/checkers/checkers_test.go#L63

So any gocritic default run like in gocritic, as expained in https://github.com/go-critic/go-critic#usage:

# Run all stable checkers on current dir and all its childs recursively:
gocritic check ./...

And a default gocritic run inside golangci-lint are using the same checks.

A note should be added somewhere IMHO in the code until we find a way to get this list programatically from lintpack/gocritic.