Replace redis library in redis store implementation

[AlexeyBelezeko]

This pull request replaces redigo with redis-go in Redis store implementation. Such change provides additional flexibility by using Redis client interface to construct a new store, which adds the possibility to use RedisCluster or RedisMock.

[lilrn]

This is a good suggestion

[rubensayshi]

@appleboy this just got bumped up quite a bit in priority as redigo deprecated the version which you're using and it's breaking any go list actions ...

go list -u -m -json all
go list -m: github.com/gomodule/[email protected]+incompatible: retracted by module author: Old development version not maintained or published.
go list -m: github.com/gin-contrib/[email protected] requires
	github.com/gomodule/[email protected]+incompatible: missing go.sum entry; to add it:
	go mod download github.com/gomodule/redigo

I opened a fresh PR which is rebased and uses the latest versions: #148

[fgm]

Redigo has a maintained branch in the 1.8.x series (currently 1.8.9), updated not long after this issue. Probably better to stay on it and just depend on the live version (1.8.9) instead of the older pre-module deprecated one (2.0.0).