Suggestion: migrate from Dep to Go Module

[itscaro]

Since Go module is experimental in 1.11, we should wait for 1.12 to have this feature as official.

Expected Behaviour

Go module will be used to keep track of dependencies and avoid the need of GOPATH

Current Behaviour

dep is currently used

WIP

https://github.com/openfaas/faas-cli/compare/master...itscaro:go-module

[itscaro]

Derek add label: proposal

[alexellis]

Derek add label: proposal

[alexellis]

Derek add label: blocked

[alexellis]

Please see notes on: https://github.com/openfaas/faas/issues/875

[alexellis]

I've upgraded to Go 1.11 but continue to use dep -> https://github.com/openfaas/faas-cli/releases/tag/0.8.0

[itscaro]

Updated the branch so that there is only ref to go module, since 1.11 is already on master