Changed linter and lint fixes

[richardcase]

Description

Changed the linter from gometalinter to GolangCI-Lint as it is faster
and the configuration and output are better.

Fixed issues highlighted by the new linter. The following
linters have been disabled and should be enabled in the future:

• gocyclo
• lll
• gosec

This is further to work already carried out in #206

Checklist

• Code compiles correctly (i.e make build)
• Added tests that cover your change (if possible)
• All tests passing (i.e. make test)
• Added/modified documentation as required (such as the README)
• Added yourself to the humans.txt file

[errordeveloper]

CI seems unhappy - any ideas? IIRC, we have CGO disabled, so is that why we are getting some CGO weirdness there?

[richardcase]

@errordeveloper - yeah i thought from the message it may bbe because CGO is disabbled. I'm going to have a look this morning.

[errordeveloper]

We have CGO_ENABLED=0, but only when build releases:

.goreleaser.yml:      - CGO_ENABLED=0

[errordeveloper]

I've enabled GolangCI, let's see how it works. But for now, I'd just stick to what we have, I don't think gometalinter is that slow. If we could just make GolangCI do its job, it'd be fine by me to use it along the side with current CircleCI setup.

[errordeveloper]

Here is an idea: let's merge this changes, but without enabling new linter in CircleCI =)

[errordeveloper]

I like this, now we have some CI redundancy and GolangCI reported before CircleCI jobs finished, because it doesn't run unit tests.

[richardcase]

Nice, thats an even better idea