Upgrade dependency "github.com/tendermint/tm-db"

[Morty-luo]

It seems that MinterTeam/minter-go-node directly depends on github.com/tendermint/tm-db@v0.6.6. But module github.com/tendermint/tm-db at version v0.6.6 uses replace directive to replace dependency github.com/tecbot/gorocksdb with github.com/roysc/gorocksdb.

https://github.com/MinterTeam/minter-go-node/blob/master/go.mod#L27

github.com/tendermint/tm-db v0.6.6

https://github.com/tendermint/tm-db/blob/v0.6.6/go.mod(line 12&22)

github.com/tecbot/gorocksdb v0.0.0-20191217155057-f0fad39f321c
replace github.com/tecbot/gorocksdb => github.com/roysc/gorocksdb v1.1.1

According to Go Modules wikis, replace directives in modules other than the main module are ignored when building the main module.
It means such replace usage in dependency's go.mod cannot be inherited when building main module. And it turns out that MinterTeam/minter-go-node indirectly relies on github.com/tecbot/gorocksdb, which is different from the replaced dependency tendermint/tm-db needed.

https://github.com/MinterTeam/minter-go-node/blob/master/go.mod#L97

github.com/tecbot/gorocksdb v0.0.0-20191217155057-f0fad39f321c // indirect

To avoid such inconsistency, the best approach is bumping the version of github.com/tendermint/tm-db since the latest release(v0.6.7) of github.com/tendermint/tm-db has eliminated the replace usage in go.mod.