Update module github.com/gorilla/mux to v1.8.1

go.mod

go.sum

vendor/github.com/gorilla/mux/.editorconfig

vendor/github.com/gorilla/mux/.gitignore

vendor/github.com/gorilla/mux/AUTHORS

vendor/github.com/gorilla/mux/LICENSE

vendor/github.com/gorilla/mux/Makefile

vendor/github.com/gorilla/mux/README.md

vendor/github.com/gorilla/mux/doc.go

vendor/github.com/gorilla/mux/go.mod

vendor/github.com/gorilla/mux/mux.go

vendor/github.com/gorilla/mux/regexp.go

vendor/github.com/gorilla/mux/route.go

vendor/modules.txt