Add MongoDB dependencies to vendor

go.mod

go.sum

vendor/github.com/go-stack/stack/.travis.yml

vendor/github.com/go-stack/stack/LICENSE.md

vendor/github.com/go-stack/stack/README.md

vendor/github.com/go-stack/stack/stack.go

vendor/github.com/golang/snappy/.gitignore

vendor/github.com/golang/snappy/AUTHORS

vendor/github.com/golang/snappy/CONTRIBUTORS

vendor/github.com/golang/snappy/LICENSE

vendor/github.com/golang/snappy/README

vendor/github.com/golang/snappy/decode.go

vendor/github.com/golang/snappy/decode_amd64.go

vendor/github.com/golang/snappy/decode_amd64.s

vendor/github.com/golang/snappy/decode_other.go

vendor/github.com/golang/snappy/encode.go

vendor/github.com/golang/snappy/encode_amd64.go

vendor/github.com/golang/snappy/encode_amd64.s

vendor/github.com/golang/snappy/encode_other.go

vendor/github.com/golang/snappy/snappy.go