Set linter output format for local/CI

[jholdstock]

No description provided.

[dnldd]

CI generated this:

 ./run_tests.sh: 20: ./run_tests.sh: [[: not found
+ OUT_FORMAT=colored-line-number
+ golangci-lint run --disable-all --deadline=10m --out-format=colored-line-number --enable=gofmt --enable=golint --enable=vet --enable=gosimple --enable=unconvert --enable=ineffassign

notice the not found in there?

[jholdstock]

Sorted

[dnldd]

Nice!

[jholdstock]

Copying from Matrix, a quick demo of what this PR does:

This is a failing linter without 246 (This PR)
https://github.com/jholdstock/dcrpool/actions/runs/291068415
The only thing github can see is that a process ended with exit code != 0

This is the same failure with 246
https://github.com/jholdstock/dcrpool/actions/runs/291073141
Github can now interpret the issue - unreachable code warning from govet linter

Because github has this deeper understanding of build errors, you can see exactly why builds failed from directly within PRs, etc, without having to dig through logs

local CLI coloring is still enabled both before and after 246

I think the links above will go stale eventually. Github doesnt store build logs forever