Use gometalinter installer for all golang syntax checkers

[jayvdb]

Most of the go linters are installed using gometalinter which keeps a versioned copy of the dependencies.

However we still have the manual install of

go get -u sourcegraph.com/sqs/goreturns
go get -u github.com/BurntSushi/toml/cmd/tomlv

tomlv isnt a linter of go language, so it wont be suitable for gometalinter, but it is less likely to break with go versions because it doesnt check go syntax which changes with each golang version and doesnt depend on golang syntax parsers which improves (aka breaks) with each golang version.

goreturns could be proposed to gometalinter, allowing us to maintain all go syntax linters via gometalinter

(See #2599 for removal of unnecessary go gets)

[jayvdb]

Another go bear to potentially add to gometalinter #1649

[jayvdb]

goreturns proposed upstream at alecthomas/gometalinter#568