Make code golint compliant

[hanzei]

$ make golint
Running lint
env GO111MODULE=off /usr/bin/go get golang.org/x/lint/golint
/home/sumacheb/go/bin/golint -set_exit_status ./...
server/plugin.go:26:2: exported const PostMeetingKey should have comment (or a comment on this block) or be unexported
server/plugin.go:35:6: exported type IClient should have comment or be unexported
server/plugin.go:44:6: exported type Plugin should have comment or be unexported
server/plugin.go:57:1: exported method Plugin.OnActivate should have comment or be unexported
Found 4 lint suggestions; failing.
make: *** [Makefile:80: golint] Error 1

[hanzei]

I've updated the PR description, because some of the issues got fixed.

Thanks @ivenk for your continuous work on this.

[hanzei]

@kosgrz Almost! Do you want to take care of the rest?

[kosgrz]

@hanzei Sure! I'll take care of the rest today or tomorrow 👍.