Replace gometalinter with golangci-lint

[pedropombeiro]

Problem

gometalinter is very slow compared to golangci-lint. In order to speed up CI builds, we should migrate to the faster tool.

Context: https://status-im.slack.com/archives/C8QP8S5UH/p1527617461000018

time make lint
lint

real    1m4.286s
user    3m21.009s
sys     0m20.387s

Implementation

• Update Makefile to install and run golangci-lint.
• Compare time take to install and run lint tool, before and after upgrade.

Acceptance Criteria

The new tool runs in a functionally equivalent way to gometalinter. The new tool is faster than the existing solution.

[pedropombeiro]

Took a preliminary look at golangci-lint and found the following differences compared to gometalinter:

• 4.5x faster
• Speed is blazing fast compared to gometalinter and would be great having this soon on our CI to relieve pressure
• Doesn't support customizing gas linter
• Doesn't support misspell linter

real    0m14.062s
user    0m43.052s
sys     0m4.261s

On the other hand, it seems to produce more useful results than gometalinter. An example:

@divan @adambabik do you have any suggestions regarding the above limitations? E.g. should we run the misspell linter separately in the make lint target? gasv2 linter is just gas -fmt=csv, is this required?

[adambabik]

In my opinion, gas is still too experimental and I would get rid of it. We can run misspell individually, not a problem. As long as it will be encapsulated in make lint target.