With Go 1.14 (https://tip.golang.org/doc/go1.14#go-command), it now automatically checks for the existence of a vendor directory. So there is no need to explicitly set the `-mod=vendor` flag.
config.json
This is the system configuration file for your Mattermost server. Settings are specific to different editions of Mattermost. Please read the documentation before making changes: https://about.mattermost.com/default-config-docs/